JP2011239603A - Charge and discharge system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charge and discharge system with high charge and discharge efficiency even after simplification of a circuit.SOLUTION: A charge and discharge system 10 includes: a power supply part (PV 11); a storage part (EDLC 12) composed of a plurality of cells charged for each cell by the power supply part; a load part (LED 13) receiving power supply from the storage part; and a control part 14 switching connection of the plurality of cells to charge the storage part at a voltage exceeding a rated cell voltage and to perform discharge according to the rated voltage of the load part.

Description

  The present invention relates to a charge / discharge system, and more particularly to a charge / discharge system suitable for use in a solar system using an electric double-layer capacitor (EDLC) charged as a secondary battery.

  In recent years, solar systems using photovoltaic power generation have attracted attention, and solar systems with higher charge / discharge efficiency are required. Photovoltaic power generation is a power generation system that uses solar cells that absorb solar energy and convert it into electricity. A solar cell is a semiconductor that generates electricity according to the amount of solar radiation when sunlight is obtained, and is also called PV (Photovoltaic). Since the solar system itself does not have a power storage function, the solar system is configured to be able to supply effective power regardless of whether there is sunshine or not by using it together with a secondary battery such as EDLC.

  In the solar system described above, Patent Documents 1, 2, and 3 introduce methods for efficiently storing power from a solar cell to a capacitor. According to Patent Documents 1, 2, and 3, all disclose a technique for monitoring the state of a solar battery or a load and switching a combination of series-parallel connection of cells of the solar battery with a switch.

JP 2000-60021 (paragraphs [0006] to [0009], FIG. 1) JP-A-6-296333 (paragraphs [0006] to [0007], FIG. 1) International Publication No. 2004-109890 (page 3, line 12 to page 6, line 4, FIG. 1)

  By the way, in the solar system described above, charging is made inefficient as there is a potential difference between the output voltage of the solar battery and the charging voltage of the secondary battery. In order to charge this efficiently, a converter that boosts or lowers the charging voltage and performs charging or a step-up / down circuit constituted by a dedicated IC is required. Also, in the case of discharge, if there is a potential difference between the output voltage of the secondary battery and the rated voltage of a DC load such as an LED (Light Emitting Diode), for example, the discharge voltage can be discharged efficiently and stably. A step-up / step-down circuit that boosts or lowers the voltage is required. For this reason, the circuit scale has increased, which has been a hindrance in realizing downsizing and cost reduction.

  The present invention has been made in view of the above problems, and an object thereof is to provide a charge / discharge system having high charge / discharge efficiency even if the circuit is simplified.

  In order to solve the above-described problems, a charge / discharge system according to the present invention includes a power supply unit, a power storage unit composed of a plurality of cells charged in units of cells by the power supply unit, and a load unit that receives power from the power storage unit And a control unit that switches the connection of the plurality of cells so that the power storage unit is charged with a voltage that exceeds a rated cell voltage and is discharged in accordance with the rated voltage of the load unit. To do.

  In the charging / discharging system of the present invention, the control unit monitors a series-parallel connection switching circuit that performs connection switching of the plurality of cells connected in series and parallel, and monitors output voltages of the power source unit and the power storage unit, A controller that performs connection switching of the plurality of cells by a series-parallel connection switching circuit.

  Further, in the charge / discharge system of the present invention, the controller charges cells connected in series according to a minimum number of serial connections that can be fully charged determined by a rated cell voltage, and a charge end voltage of the cells connected in series is predetermined. When one of the cells connected in series is exceeded, one of the cells connected in series is switched to parallel connection, and the end-of-charge voltage is controlled so as not to exceed a value obtained by multiplying the minimum series connection number and the rated cell voltage. It is characterized by.

  In the charging / discharging system of the present invention, the controller reads a preset rated voltage of the load unit, and connects the cells constituting the power storage unit in series-parallel connection so that the read rated voltage is obtained. When discharge is performed by switching, and the total voltage of the cells connected in series drops to a predetermined value, the one cell connected in parallel is switched to the cell connected in series, and all the cells are connected in series. The discharge is terminated when the voltage falls to the predetermined value in a state where

  Further, in the charge / discharge system of the present invention, the output voltage of the power supply unit or the power storage unit is connected between the power source unit and the power storage unit, or between the power storage unit and the load unit, or both. A step-up / step-down circuit that keeps the output voltage constant within the allowable range of fluctuations, and depending on the rated cell voltage of the power storage unit or the rated voltage of the load unit, the controller may charge or discharge by the series-parallel connection switching circuit. The control is switched to charge / discharge control by the step-up / step-down circuit.

  The charging / discharging system of the present invention includes a solar battery, a secondary battery that is charged in units of cells by the solar battery and configured by a plurality of cells, a DC load that receives power from the secondary battery, and the secondary battery. Prior to charging / discharging the secondary battery, a day / night determination is made based on the output voltage of the solar battery, and when it is determined to be daytime, the secondary battery is charged at a voltage exceeding the rated voltage of the cell and determined to be night. And a control device that switches connection of the plurality of cells so that the secondary battery is discharged with an output voltage that matches the rated voltage of the DC load.

  ADVANTAGE OF THE INVENTION According to this invention, even if it simplifies a circuit, the charging / discharging system which has high charging / discharging efficiency can be provided.

It is a block diagram which shows the structure of the charging / discharging system which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the control part of the charging / discharging system which concerns on the 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the control part of the charging / discharging system which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the connection switching operation | movement of the cell at the time of charge of the charging / discharging system which concerns on the 1st Embodiment of this invention. It is the figure which showed typically the connection switching operation of the cell at the time of charge of the charging / discharging system which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the connection switching operation | movement of the cell at the time of discharge of the charging / discharging system which concerns on the 1st Embodiment of this invention. It is the figure which showed typically the connection switching operation | movement of the cell at the time of discharge of the charging / discharging system which concerns on the 1st Embodiment of this invention. It is the figure which showed the discharge operation of the charging / discharging system which concerns on the 1st Embodiment of this invention on the time series. It is a block diagram which shows the structure of the charging / discharging system which concerns on the 2nd Embodiment of this invention. It is the figure which showed the discharge operation of the charging / discharging system which concerns on the 2nd Embodiment of this invention on the time series.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the accompanying drawings. Note that the same number is assigned to the same element throughout the description of the embodiment.

(Configuration of the first embodiment)
FIG. 1 is a block diagram showing a configuration of a charge / discharge system according to the first embodiment of the present invention. According to FIG. 1, the charge / discharge system 10 includes a power supply unit 11, a power storage unit 12, a load unit 13, a control unit 14, and charge / discharge switches 15 and 16.

  Here, a solar system is illustrated as the charge / discharge system 10, and the power supply unit 11 is described as PV, the power storage unit 12 is EDLC, and the load unit 13 is an LED. The EDLC 12 is charged in units of cells by the PV 11 and turns on the LED 13. The control unit 14 performs switching control of connection of a plurality of cells so that the EDLC 12 configured by connecting a plurality of cells in series and parallel is charged with a voltage exceeding the rated cell voltage and discharged according to the rated voltage of the LED 13. . For example, a jumper switch (not shown) is connected to the control unit 12 via a line 17 and is set by the jumper switch or the like. The open voltage of the PV 11, the rated voltage of the single cell constituting the EDLC 12, and the rated load of the LED Data such as voltage is taken in and the above control is performed.

  The charge / discharge switches 15 and 16 are switch circuits configured by, for example, FETs (Field Effect Transistors) that switch between charge and discharge under the control of the control unit 14. The charge / discharge switches 15 and 16 realize sharing of a serial / parallel switching circuit 142, which will be described later, used together during charge / discharge.

  For example, as shown in FIG. 2, the control unit 12 includes a series-parallel connection switching circuit 141 and a controller 142. The series / parallel connection switching circuit 141 has a well-known circuit configuration disclosed in, for example, Patent Documents 1, 2, and 3 described above, which performs connection switching of a plurality of cells connected in series and parallel that constitute the EDLC 12. The controller 142 has a function of monitoring output voltages of the PV 11 and the EDLC 12 and performing connection switching of a plurality of cells of the EDLC 12 by the series / parallel connection switching circuit 141.

  The controller 142 is constituted by, for example, a microprocessor including a memory, and the above functions are executed under program control recorded in the memory.

  The controller 142 performs switching of the series-parallel connection of a plurality of cells constituting the EDLC 12, and also performs switching of charging / discharging of the charging / discharging switches 15 and 16 described above. Here, all are controlled by one controller 142, but charge / discharge switching may be controlled by independent controllers. In the first embodiment, the control unit 14 is illustrated as a separate body from the EDLC 12, but may be incorporated in the EDLC 12.

(Operation of the first embodiment)
3, 4, and 6 are flowcharts showing the operation of the charge / discharge system 10 according to the first embodiment of the present invention. 3 shows the overall operation, FIG. 4 shows the cell switching operation of the EDLC 12 during charging, and FIG. 6 shows the cell switching operation of the EDLC 12 during discharging.

  According to FIG. 3, the control unit 14 (controller 142) first takes in data such as the open voltage of the PV 11 and the rated voltage of the LED 13 which are selected and set by the operator via a jumper wire or the like, and applies to subsequent calculations. The initial setting is performed (step S31). This initial setting determines the number of cells connected in series at the time of charge / discharge described later.

  Charge / discharge control is started after the above initial setting, and the controller 142 first monitors the output voltages of the PV 11 and the LED 13 (step S32). Then, the day / night mode is determined by checking the open voltage of the PV 11 (step S33). For example, when the initially set open voltage of the PV 11 is 15V, it is determined as a day mode in which charging is performed when the monitoring voltage is 15V or higher, and a night mode in which discharging is performed when the monitoring voltage is lower than 15V.

  When the daytime mode is determined (step S33 “daytime mode”), the controller 142 controls the charge / discharge switches 15 and 16 to stop the discharge that has been performed so far (step S34) and perform charging. The series-parallel connection switching circuit 141 is controlled to switch the series-parallel connection of a plurality of cells constituting the EDLC 12 (step S35). Here, the controller 142 switches the cell connection so as to charge the EDLC 12 with a voltage exceeding the rated cell voltage, and performs charging (step S36). Details of the cell connection switching at the time of charging will be described later with reference to FIGS.

  On the other hand, when the night mode is determined (step S33 “night mode”), the controller 142 controls the charge / discharge switches 15 and 16 to stop charging (step S37), and performs series-parallel connection for discharging. The switching circuit 141 is controlled to switch the series-parallel connection of a plurality of cells constituting the EDLC 12 (step S38). Here, the controller 142 switches the connection of the cells of the EDLC 12 so as to discharge in accordance with the rated voltage of the LED 13, and performs discharge (step S39). Details of the cell connection switching at the time of discharging will be described later with reference to FIGS.

  The cell connection switching operation during charging will be described in detail with reference to the flowchart of FIG.

  First, the controller 142 reads the open voltage of the PV 11 and the rated cell voltage value of the EDLC 12 set by a jumper wire or the like via the line 17 (step S351). Then, the minimum number of cells that can be fully charged determined by the rated cell voltage of the EDLC 12 is determined so that the read voltage of the PV 11 is 80% of the open-circuit voltage of the PV 11 (maximum charging efficiency is exhibited). Then, the serial / parallel connection switching circuit 141 is controlled to switch the constituent cells of the EDLC 12 in series according to the number of connections, and charging of the series connected cells is started (step S352).

  For example, if the open voltage of PV11 is 15V, the rated voltage of EDLC12 is 10V (single cell 2.5V), and the rated voltage of LED13 is 10V, 80% of the open voltage of PV11 is 12V. Since the value divided by 2.5V is 4.8, the minimum number of series connections is 4.

  Subsequently, the controller 142 monitors the output voltage of the PV 11 (step S353). Here, when the charge end voltage of the cells connected in series exceeds 80% of the open voltage of PV11 (step S354 “≧”), the controller 142 controls the series-parallel connection switching circuit 141, One of the cells connected in series first is switched to parallel connection (step S355), and finally charged with the minimum number of series. The controller 142 controls the charge end voltage so that the charge end voltage of the cells connected in series does not exceed a value obtained by multiplying the minimum number of series connections and the rated cell voltage of the single cell.

  FIG. 5 schematically shows a specific example of cell connection switching at the time of charging when the EDLC 12 is configured by 12 cells in 4 series and 3 parallels.

  According to FIG. 5, as shown in FIG. 5A, in the EDLC 12, all of the 12 single cells are connected in series immediately after charging when the charge amount is zero. Also, as shown in (b), if this is charged to 12V, all the cells remain connected in series until each cell is charged by 1V. Subsequently, as shown in (c), after charging up to 12V, the controller 142 controls the series / parallel connection switching circuit 141 to switch only one cell to the parallel connection. Here, each cell is charged to 1.1 V, and the total number of series connections is 11 in which 10 single cells and 1 two parallel cells are connected in series.

  And as shown in (d), if it charges to 12V, it will switch to 1 cell parallel. Here, it is assumed that each single cell is charged by 1.2 V, and the total number is 10 series in which nine single cells and three parallel cells are connected in series. In addition, if it charges to 12V, after that, parallel switching will be repeated cell by cell. That is, as shown in (e), if each single cell is charged to 2.4 V, the total number is 5 in which 4 single cells and 8 parallel cells are connected in series. Then, as shown in (f), finally, charging is performed until the night mode is reached with the minimum series number of 4 series and 3 parallel. The end-of-charge voltage at this time is 10V.

  In addition, when the cells constituting the EDLC 12 remain halfway, for example, when there is a place where the minimum number of serial connections is 5 cells with respect to 4 cells, as shown in (g), the end-of-charge voltage is 10V. When this happens, it is necessary to switch the remaining cells and the cells being charged in order.

  Next, the cell connection switching operation during discharging will be described in detail with reference to the flowchart of FIG.

  First, the controller 142 reads the rated voltage of the LED 13 set by a jumper wire or the like via the line 17 (step S381). According to the rated voltage of the LED 13 set here, the upper and lower limits of ± 1.5 V, for example, within the allowable discharge voltage range are automatically set (step S382). Then, the controller 142 performs connection switching of the cells constituting the EDLC 12 so as to obtain the rated voltage read by controlling the series / parallel switching circuit 141 (step S383). Here, it is set as the cell connection structure of 4 series 3 parallel at the time of a full charge.

  The controller 142 monitors the output voltage of the EDLC 12 (step S384). As a result of the voltage monitoring, when the total output voltage value of the cells connected in series has reached the lower limit value of 8.5 V or less (step S385 “≦”), the controller 142 controls the series-parallel connection switching circuit 141. Then, one of the parallel connection cells of the EDLC 12 is destroyed and connection switching is performed to distribute the remaining cells connected in series, and the remaining cells are connected in parallel to the cells connected in series (step S386). Then, discharging is performed, and the above-described operation of step S386 is repeatedly executed every time the output voltage of the EDLC 12 becomes lower than the lower limit value. All the cells are connected in series, and the discharge is terminated when the lower limit value is 8.5V.

  FIG. 7 schematically shows a specific example of cell connection switching at the time of discharge when the EDLC 12 is composed of 12 cells in 4 series and 3 parallels.

  According to FIG. 7, immediately after the discharge, as shown in (a), the controller 142 controls the series / parallel connection switching circuit 141 to switch the connection so that the output voltage of the EDLC 12 becomes the set rated voltage of 10V. Do. Here, it is set as the connection structure of 4 series 3 parallel at the time of full charge, and all the single cells which comprise EDLC12 have a capacity | capacitance of 2.5V.

  Next, as shown in (b), it is assumed that the output voltage of the EDLC 12 is lowered by discharge and reaches a lower limit of 8.5V. Note that the capacity of each single cell constituting the EDLC 12 is 2.1V. At this time, as shown in (c), the connection switching is performed in which the parallel connection cells of the EDLC 12 are broken down into the remaining cells connected in series. The surplus cells are connected in parallel to the cells connected in series. That is, the cell connection configuration of the EDLC 12 is 5 series and 2 parallel, and can output a voltage of 10.5V.

  Subsequently, as shown in (d), when the capacity of each single cell drops to 1.7 V and the output voltage of the EDLC 12 reaches 8.5 V that is the lower limit voltage again due to discharge, the controller 142 is connected in series-parallel connection. The switching circuit 141 is controlled to switch the cell connection configuration of the EDLC 12 between 6 series and 2 parallel as shown in (e). According to this connection configuration, the EDLC 12 can supply a voltage of 10.2 V to the LED 13. Further, as shown in (f), when the capacity of each single cell is reduced to 1.4 V and the output voltage of the EDLC 12 reaches the lower limit value of 8.5 V due to further discharge, the controller 142 is connected in series-parallel connection. The switching circuit 141 is controlled to switch the cell connection configuration of the EDLC 12 to 7 series shown in (g), and the surplus cells are connected in parallel and added to the series connected cells. According to this connection configuration, a voltage of 9.8 V can be supplied to the LED 13.

  Similarly, as shown in (h), when the capacity of each single cell drops to 1.2 V and the output voltage of the EDLC 12 reaches 8.5 V that is the lower limit voltage again, the controller 142 switches the series-parallel connection. The circuit 141 is controlled to repeat the operation of breaking the cells connected in parallel and connecting them in series. According to this connection configuration, the EDLC 12 can supply a voltage of 10.8 V to the LED 13. As shown in (i), the above operation is repeated until all the cells connected in series are disrupted and the total of the cells connected in series is 8.5 V or less.

  The discharge characteristics based on the above-described control are shown in FIG. FIG. 8 shows a discharge curve when the output voltage of the EDLC 12 is scaled on the vertical axis and the lighting time of the LED 13 is scaled on the horizontal axis. In FIG. 8, according to the graph shown on the left, as the lighting time of the LED 13 elapses, the output voltage of the EDLC 12 gradually decreases, and when the lighting time 2S elapses, 2 V at which the LED 13 cannot be turned on is set. Divide. On the other hand, according to the graph shown on the right, repeated discharge is possible by switching the connection so that the number of series connection of the constituent cells of the EDLC 12 is increased at a point of 2V. Here, it is possible to break down the cells connected in parallel, connect all the cells in series, and repeatedly discharge until the total of the cells connected in series is 2V or less.

(Effects of the first embodiment)
According to the charge / discharge system 10 according to the first embodiment described above, the control unit 14 (controller 142) charges the power storage unit (EDLC 12) with a voltage exceeding the rated cell voltage, and the load unit (LED 13) is rated. The connection of a plurality of cells is switched so as to discharge in accordance with the voltage. For this reason, there is no need to boost the power storage unit (EDLC12) that is equal to or higher than the rated voltage of the power supply unit (PV11), and therefore the circuit between the power supply unit (PV11) and the power storage unit (EDLC12) is simplified. The Moreover, since the rated voltage of the load unit (LED13) can be adjusted in units of cells of the power storage unit (EDLC12), the circuit between the power storage unit (EDLC12) and the load unit (LED13) is simplified. Thus, even if the circuit is simplified, a charge / discharge system having high charge / discharge efficiency can be provided. In addition, since the number of circuit components is reduced, it is possible to contribute to size reduction and cost reduction.

  The present invention is particularly effective when applied to a solar system. In addition to the above-described downsizing and cost reduction, the voltage adjustment is performed by switching the cells of the power storage unit (EDLC 12), so that noise is generated. Therefore, a solar system having high reliability can be provided.

(Configuration of Second Embodiment)
FIG. 9 is a block diagram showing the configuration of the charge / discharge system 10 according to the second embodiment of the present invention. 9, the difference from the first embodiment shown in FIG. 1 is that step-up / down circuits 18 and 19 are added between the EDLC 12 and the charge / discharge switches 15 and 16, respectively. The step-up / down circuit 18 is used for charging, and the step-up / down circuit 19 is used for discharging. Other configurations are the same as those of the first embodiment. Here, the step-up / step-down circuits 18 and 19 are combined into one, but the cells constituting the EDLC 12 may be provided in units depending on the capacity of the PV 11 or the rated voltage of the LED 13. Further, two step-up / step-down circuits 18 and 19 are not necessarily required for charging / discharging, and at least one for boosting / discharging is sufficient. Further, the single step-up / step-down circuit 18 or 19 may be shared and used for charging / discharging.

(Operation of Second Embodiment)
The step-up / step-down circuits 18 and 19 are circuits that maintain the output voltage constant within the allowable variation range of the output voltage of the PV 11 or EDLC 12, and are commercially available as converters or dedicated ICs. The controller 142 switches from charge / discharge control by the series / parallel connection switching circuit 141 to charge / discharge control by the step-up / step-down circuits 18 and 19 depending on the rated cell voltage of the EDLC 12 or the rated voltage of the LED 13. As a result, the output can be kept constant within the allowable range of fluctuations in the output voltages of the PV 11 and the EDLC 12.

  FIG. 10 shows discharge characteristics that change due to the addition of the step-up / step-down circuit 19. Here, the case where the input voltage range to the step-up / down circuit 19 (the fluctuation range of the output voltage of the power storage unit 12) is 2 to 5 V and the step-up / down circuit 19 rated at 5 V is connected is illustrated. In FIG. 10, the graph shown on the left is the discharge characteristic according to the first embodiment, and fluctuates to the upper limit with 2V as the boundary. On the other hand, according to the graph shown on the right, it can be seen that the output of 5 V is maintained constant within the allowable range of fluctuation of the output voltage of the power storage unit 12.

(Effect of 2nd Embodiment)
According to the charging / discharging system 10 according to the second embodiment of the present invention, the control unit 14 (controller 141) is connected in series or parallel according to the rated cell voltage of the power storage unit (EDLC 12) or the rated voltage of the load unit (LED 13). From the charge / discharge control by the connection switching circuit 141, it is connected between the power supply unit (PV11) and the power storage unit (EDLC12), between the power storage unit (EDLC12) and the load unit (LED13), or both. Switching to charge / discharge control by the step-up / step-down circuits 18 and 19 that keeps the output voltage constant within the permissible fluctuation range of the output voltage of the unit (PV11) or the power storage unit (EDLC12). For this reason, by using the series / parallel connection switching circuit 141 and the step-up / step-down circuits 18 and 19 in combination, it is possible to quickly charge by power charging at the time of charging, and at the time of discharging, if the fluctuation is within an allowable range Since the voltage can be kept constant, more efficient charging / discharging becomes possible.

  In the first and second embodiments described above, a solar system using a solar cell as the power supply unit 11 has been illustrated. However, the power supply unit 11 is not limited to the solar system, and the power supply unit 11 is compatible with EDLC as in the solar cell. A commercial power source obtained by utilizing hydroelectric power generation may be used. The power storage unit 12 is not limited to the EDLC, and may be any secondary battery that can be charged and discharged in units of cells. Further, the load unit 13 is not limited to the LED, and can be applied to all DC loads.

  As mentioned above, although this invention was demonstrated using embodiment, it cannot be overemphasized that the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiments. Further, it is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Charging / discharging system, 11 ... Power supply part (PV), 12 ... Power storage part (EDLC), 13 ... Load part (LED), 14 ... Control part, 17 ... Line , 15, 16 ... charge / discharge switch, 18, 19 ... buck-boost circuit, 141 ... series-parallel connection switching circuit, 142 ... controller

Claims (6)

A power supply,
A power storage unit composed of a plurality of cells charged in units of cells by the power source unit,
A load unit that receives power from the power storage unit;
The power storage unit is charged at a voltage exceeding a rated cell voltage, and a control unit that switches connection of the plurality of cells so as to discharge in accordance with the rated voltage of the load unit;
A charge / discharge system comprising: The controller is
A series-parallel connection switching circuit for switching the connection of the plurality of cells connected in series and parallel;
A controller that monitors output voltages of the power supply unit and the power storage unit, and performs connection switching of the plurality of cells by the series-parallel connection switching circuit;
The charge / discharge system according to claim 1, comprising: The controller is
The cells connected in series are charged in accordance with the minimum number of series connections that can be fully charged determined by the rated cell voltage, and when the end-of-charge voltage of the cells connected in series exceeds a predetermined value, the cells connected in series 3. The charge / discharge system according to claim 2, wherein one is switched to a parallel connection, and the charge end voltage is controlled so as not to exceed a value obtained by multiplying the minimum number of series connections and the rated cell voltage. The controller is
Read the rated voltage of the load unit set in advance, and perform discharge by switching the series-parallel connection of the cells constituting the power storage unit so that the read rated voltage, the total of the cells connected in series When the voltage drops to a predetermined value, the one cell connected in parallel is switched to the series connected cell, and the discharge occurs when the voltage drops to the predetermined value with all cells connected in series. The charge / discharge system according to claim 2, wherein the charging / discharging system is terminated. Connected between the power supply unit and the power storage unit, or between the power storage unit and the load unit, or both, and the output voltage is kept constant within the allowable range of fluctuation of the output voltage of the power supply unit or the power storage unit. With a buck-boost circuit to maintain
The controller is
The charge / discharge control by the step-up / step-down circuit is switched from the charge / discharge control by the series / parallel connection switching circuit depending on the rated cell voltage of the power storage unit or the rated voltage of the load unit. The charge / discharge system according to any one of 4. Solar cells,
A secondary battery that is charged in units of cells by the solar battery and is composed of a plurality of cells;
A DC load that receives power from the secondary battery;
Prior to charging / discharging the secondary battery, the day / night determination is performed based on the output voltage of the solar battery, and when the day is determined, the secondary battery is charged at a voltage exceeding the rated voltage of the cell, A controller for switching the connection of the plurality of cells so as to discharge the secondary battery with an output voltage that matches the rated voltage of the DC load, if determined;
A charge / discharge system characterized by comprising:

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