Rechargeable battery system

Abstract

To provide a solar system using a secondary battery in which the secondary battery can be used until a desired end of lifetime thereof so as to reduce costs.SOLUTION: A system using a secondary battery includes: a lithium ion battery 3 used as a master; and a lead battery 4 used as a slave in which a reduction of the charge capacity due to repetition of charging and discharging is more than that in the lithium ion battery 3. An overall controller 10 consisting of a controller 7 and a battery control unit 6 charges the lithium ion battery 3 prior to the lead battery 4; and discharges the lithium ion battery 3 prior to the lead battery 4.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to the technical field of a secondary battery usage system including a plurality of secondary batteries with different rates of decrease in charge capacity due to repeated charging and discharging.

Background Art

[0002] Today, there is known a so-called solar lighting device (driving device) that performs lighting and display by using the power generated by a solar cell during the day to light (drive) an LED (light-emitting diode, corresponding to an example of the "driving unit" of the present invention) at night. Such a device generally includes a solar cell that generates electricity by receiving solar energy, a secondary battery that charges the electricity generated by this solar cell, and a driving unit that is driven by receiving discharge from this secondary battery (see, for example, Patent Document 1). And the secondary battery used in this device needs to be rechargeable repeatedly, and a lead battery (lead storage battery) has been widely used for a long time as this secondary battery.

[0003] However, the life of a lead battery (decrease in charge capacity due to repeated charging and discharging) is not long. For example, based on the experience of the applicant of this application, when a lead battery is used alone as the power source of a solar lighting device for performing night lighting, sign display, etc., battery replacement is required in about 5 years. For this battery replacement, costs for the battery itself and labor costs for workers who perform the replacement work also occur, so there is a desire to make the period until battery replacement as long as possible.

[0004] On the other hand, in recent years, as secondary batteries, nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, etc. have come to be widely used. This type of secondary battery has the advantages of a longer life and being lighter than lead batteries, but has the problem of being expensive because it uses rare metals such as lithium.

[0005] On the other hand, there are also known systems that use both lead-acid batteries and lithium-ion batteries in combination as secondary batteries for hybrid vehicles and electric vehicles, etc., in order to bring out the unique characteristics of each type of secondary battery (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-85555 [Patent Document 2] Japanese Patent Publication No. 2018-18775 [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, in solar-powered lighting devices as described above, it is proposed to use two types of secondary batteries with different characteristics, such as lead-acid batteries and lithium-ion batteries, in combination to extend the battery replacement period as much as possible and reduce costs. However, it is necessary to consider how to charge and discharge the two types of secondary batteries with different characteristics in order to extend the replacement period, and this is the problem that the present invention aims to solve. [Means for solving the problem]

[0008] The present invention was made in view of the above circumstances and with the aim of solving these problems, and the invention of claim 1 comprises a power generation unit that generates electricity by receiving solar energy, a secondary battery that charges the electricity generated by the power generation unit, a drive unit that drives using the electricity charged by the secondary battery as a power source, and a controller connected to the power generation unit, the secondary battery and the drive unit respectively, which performs charge / discharge control of the secondary battery and power supply control of the drive unit, wherein the secondary battery comprises a first secondary battery and a second secondary battery which has a greater decrease in charge capacity due to repeated charge / discharge compared to the first secondary battery, and the controller is After sunrise, the second secondary battery is charged to 5% of its rated capacity, and then the first secondary battery is charged to full capacity. If the first secondary battery is fully charged, the second secondary battery is charged again before sunset. If the second secondary battery is charged again before sunset, the second secondary battery is discharged to 2% of its rated capacity after sunset, and then the first secondary battery is discharged. After the discharge of the second secondary battery after sunset, the charge level of the second secondary battery is measured, and if the second secondary battery is nearly fully charged, it is discharged further to 6% of its rated capacity. As a result, the replacement period for secondary batteries can be extended, leading to lower costs.

[0009] The invention of claim 2 is as follows: In claim 1, the controller makes the charging time of the first secondary battery longer than the charging time of the second secondary battery, and the discharging time of the first secondary battery longer than the discharging time of the second secondary battery. As a result, the decrease in the charging capacity due to repeated charging and discharging of the second secondary battery can be suppressed. [Effects of the Invention]

[0012] According to the present invention, the replacement period for secondary batteries can be extended, and costs can be reduced. [Brief explanation of the drawing]

[0013] [Figure 1] This is a block diagram showing the configuration of a secondary battery-using system according to the present invention. [Figure 2] This is a flowchart showing the control procedure for the battery control unit. [Figure 3] This figure shows the relationship between the cycle life and depth of discharge of a lithium-ion battery. [Figure 4] This figure shows the relationship between the cycle life and depth of discharge of a lead-acid battery. [Figure 5] This is the circuit diagram for the battery control unit. [Figure 6] This is a timing chart showing the timing of the control operations performed by the controller. [Modes for carrying out the invention]

[0014] <Basic configuration> Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a block diagram showing the configuration of a solar lighting system 1 (corresponding to the "secondary battery system" of the present invention) as a solar system in which the present invention is implemented. The basic configuration of this solar lighting system 1 includes a solar panel 2 as a power generation unit that converts solar energy into electrical energy, and a lithium-ion battery (corresponding to the "first secondary battery" of the present invention) 3 and a lead-acid battery (corresponding to the "second secondary battery" of the present invention) 4 as secondary batteries that are charged by the power generated by the solar panel 2.

[0015] Furthermore, the solar lighting system 1 includes an LED lighting device 5 as a drive unit that is powered by a lithium-ion battery 3 and a lead-acid battery 4, a battery control unit 6 connected to the lithium-ion battery 3 and the lead-acid battery 4 and controlling the charging and discharging of these lithium-ion battery 3 and lead-acid battery 4 together with a controller 7, which will be described later, and a controller 7 connected to the solar panel 2, the LED lighting device 5, and the battery control unit 6.

[0016] The solar panel 2 generates electricity during the day and sends the generated current to the controller 7. The generated current sent to the controller 7 is sent to the lithium-ion battery 3 or lead-acid battery 4 via the battery control unit 6 and charged. At night, a discharge current is sent from the lithium-ion battery 3 or lead-acid battery 4 to the controller 7 via the battery control unit 6. The discharge current sent to the controller 7 is output to the LED lighting device 5 and lights up the LED lighting device 5. Thus, the LED lighting device 5 is configured to repeat the cycle of turning on (driving) and turning off (stopping) in a 1-day cycle, and the power supply control to the LED lighting device 5, including turning on and off (including control of the lighting time) and PWM (Pulse Width Modulation) control to adjust the brightness, is performed by the controller 7. In this way, the controller 7 is similar to a general solar lighting system controller that uses one type of secondary battery currently on the market. The present invention is a controller 7 into which a battery control unit 6 is inserted, which independently determines the switching connection of two types of secondary batteries according to various conditions, and it is also possible to integrate the controller 7 and the battery control unit 6 into a single overall controller 10.

[0017] The battery control unit 6, via a switch 9 activated by a signal from a controller 8 (such as a one-chip microcontroller) provided in the battery control unit 6, selectively connects either the lithium-ion battery 3 or the lead-acid battery 4 to the controller 7, and controls the charging and discharging of the connected lithium-ion battery 3 or lead-acid battery 4.

[0018] Switch 9 is configured to select either an ab connection or an ac connection based on a signal from the controller 8. Terminal a is connected to the battery positive terminal (B+) of the controller 7 via the controller connection positive terminal (O+) of the battery control unit 6. Terminal b is connected to the positive terminal (+) of the lithium-ion battery 3 via the lithium-ion battery connection positive terminal (L+) of the battery control unit 6. Terminal c is connected to the positive terminal (+) of the lead-acid battery 4 via the lead-acid battery connection positive terminal (P+) of the battery control unit 6.

[0019] Also, the negative terminal (-) of the lithium-ion battery 3 is connected to the negative terminal for lithium-ion battery connection (L-) of the battery control unit 6. The negative terminal (-) of the lead battery 4 is connected to the negative terminal for lead battery connection (P-) of the battery control unit 6. The negative terminal for lithium-ion battery connection (L-) and the negative terminal for lead battery connection (P-) of the battery control unit 6 are respectively connected to the negative terminal for battery for controller (B-) of the controller 7 via the negative terminal for controller 7 connection (O-).

[0020] When the switch 9 is connected to a-b, the lithium-ion battery 3 is in a state of being connected to the controller 7 (ON), and the lead battery 4 is in a state of being disconnected (OFF), and only the lithium-ion battery 3 is charged or discharged. When the switch 9 is connected to a-c, the lead battery 4 is in a state of being connected to the controller 7 (ON), and the lithium-ion battery 3 is in a state of being disconnected (OFF), and only the lead battery 4 is charged or discharged.

[0021] By not directly connecting the lithium-ion battery 3 and the lead battery 4 in parallel so that they are not simultaneously ON, even when two types of secondary batteries with different electrical characteristics are used together, without separately providing a protection circuit, it is configured to reliably avoid the risk of heat generation and ignition caused by differences in the voltage values and internal resistances of the two types of secondary batteries.

[0022] The signal of the a terminal of the switch 9 is input to the controller 8 and is used for measuring the voltage of the lithium-ion battery 3 when connected to a-b. Also, the illumination output signal from the controller 7 to the LED lighting device 5 is input to the controller 8 via the illumination signal input terminal (LD) of the battery control unit 6 and is used for determining the lighting (driving) and extinguishing (stopping) of the LED lighting device 5 and for measuring the duty ratio of PWM control. Note that as the controller 8, for example, a one-chip microcomputer is used, and it has various control means such as means for setting the target discharge time and the target loop count LC described later, means for counting the loop count, and means for measuring the battery voltage.

[0023] The controller 8 is configured to set the switch 9 to either an ab connection or an ac connection. This setting result is transmitted from the controller 8 to the controller 7 through the connection status notification terminal (BI) between the controller 7 and the battery control unit 6.

[0024] <Control Method> Next, the control performed by the controller 8 will be explained based on Figures 2 to 6.

[0025] First, Figure 2 shows the control flowchart. When control starts, as an initial setting, the target number of loops LC corresponding to the load required to light up the LED lighting device 5 is set, and the counter that counts this target number of loops is reset to "zero (0)" (step S1). Although not shown in the figure, switch 9 is set to the ab connection state (Li→ON, Pb→OFF), and the Pb charge ON flag is set to 1 and the Pb discharge ON flag is set to 0.

[0026] Here, we will explain how to set the target loop count LC according to the load required to light up the LED lighting device 5. As shown in Table 1, for example, when the load of the LED lighting device 5 is 12 lighting LEDs, the load current is 1.3A, the rating of the lithium-ion battery 3 used is 24Ah, and the duty cycle that allows for a 10-year service life is 68% (from Figure 3). Therefore, the usable energy of this lithium-ion battery 3 is 16.32Ah (=24Ah × 0.68). And, since the load current is 1.3A, the usable time of the lithium-ion battery 3 (time until switching to the lead-acid battery 4) is 45,194 sec (=12.554h = 16.32Ah / 1.3A), and when a 50ms timer is used, the target loop count LC = 903,880 times (=45,194 sec / 0.05 sec).

[0027] [Table 1]

[0028] Next, it is determined whether the Pb discharge ON flag is "1" (step S2). If the Pb discharge ON flag is "1" (YES: ON), it is determined whether the LD terminal signal indicates discharge (step S3). If it is determined in step S3 that discharge is occurring (YES), the switch 9 is operated to connect to AC, turning the lithium-ion battery 3 OFF and the lead-acid battery 4 ON (step S4). In this state, the discharge of the lead-acid battery 4 is started, a timer for a first predetermined time, for example 30 minutes, is activated, and the lead-acid battery 4 is discharged for this first predetermined time (step S5). Then, the Pb discharge ON flag is set to "φ" (step S6).

[0029] Subsequently, the output voltage (Pb voltage) after the lead-acid battery 4 has been discharged for a predetermined time is measured, and the measured output voltage is set to a predetermined constant value (V R If the above is true (Step S7: YES), then the lead-acid battery 4 has remaining charge capacity, so discharge the lead-acid battery 4 for a further 90 minutes, for example (Step S8). In Step S7, the output voltage of the lead-acid battery 4 is V R If the value is less than (NO), the discharge of lead-acid battery 4 is terminated because there is no remaining charge capacity in lead-acid battery 4.

[0030] Here, if the Pb discharge ON flag is "φ" (NO) in step S2, or if the LD terminal signal is charging (NO) in step S3, the discharge of lead-acid battery 4 in step S5 is not performed.

[0031] After the additional 90 minutes of discharge of the lead-acid battery 4 in step S8 is completed, the Pb charge ON flag is checked (step S9). If the Pb charge ON flag is "1" (step S9: YES), it is determined whether the LD terminal signal is in discharge mode (step S10). If it is determined that the LD terminal signal is not in discharge mode (step S10: NO), the Pb charge ON flag is set to "φ" (step S11), and then the switch 9 is operated to connect to AC, turning the lithium-ion battery 3 OFF and the lead-acid battery 4 ON (step S12). In this state, charging of the lead-acid battery 4 is started, and a timer for a second predetermined time, for example 165 minutes (2 hours and 45 minutes), is activated, and the lead-acid battery 4 is charged for this second predetermined time (step S13).

[0032] Next, switch 9 is operated to set the ab connection, turning lithium-ion battery 3 ON and lead-acid battery 4 OFF (step S14). In this state, the duty cycle of lithium-ion battery 3 is determined by the LD terminal signal to be 20% (step S15). S15 If the determination in step S16 indicates that the duty cycle of the lithium-ion battery 3 is 20% (YES), a timer for a third predetermined time, for example 250ms, is activated, and the lithium-ion battery 3 is discharged for this third predetermined time.

[0033] If the determination in step S15 is that the duty cycle of the lithium-ion battery 3 is not 20% (NO), then it is determined in step S17 whether the duty cycle of the lithium-ion battery 3 is 50%. If the determination in step S17 is that the duty cycle of the lithium-ion battery 3 is 50% (YES), then a fourth predetermined time timer, for example 100ms, is started, and the lithium-ion battery 3 is discharged for this fourth predetermined time (step S18).

[0034] Furthermore, if the determination in step S17 indicates that the duty cycle of the lithium-ion battery 3 is not 50% (NO), then it is determined in step S19 whether the duty cycle of the lithium-ion battery 3 is 65%. If the determination in step S19 indicates that the duty cycle of the lithium-ion battery 3 is 65% (YES), then a timer for a fifth predetermined time, for example 77ms, is activated, and the lithium-ion battery 3 is discharged for this fifth predetermined time (step S20).

[0035] If the determination in step S19 indicates that the duty cycle of the lithium-ion battery 3 is not 65% (NO), a timer for a sixth predetermined time, for example 50ms, is activated (in which case the duty cycle is 100%), and the lithium-ion battery 3 is discharged for this sixth predetermined time (step S21). Note that the duty cycle of the lithium-ion battery 3 during charging is 0% (because the lighting output signal LD ​​from the controller 7 is absent during charging), so steps S15, S17, and S19 all result in (NO), and the process proceeds to step S21.

[0036] In step S9, if the Pb charging ON flag is set to "φ" (NO), or if the LD terminal signal in step S10 indicates that discharge is occurring (YES), then charging of the lead-acid battery 4 in steps S11 through S13 is not performed, and the process proceeds to step S14.

[0037] Next, it is determined whether the voltage of the lithium-ion battery 3 (Li voltage) exceeds the voltage when fully charged (upper limit voltage), for example, 14.04V (step S22). If the determination in step S22 shows that the voltage of the lithium-ion battery 3 exceeds the upper limit voltage (YES), it is determined whether the lithium-ion battery 3 is in the discharge phase (step S23). If the lithium-ion battery 3 is not in the discharge phase (i.e., in the charging phase) (step S23: NO), the switch 9 is operated to connect to AC, turning the lithium-ion battery 3 OFF and the lead-acid battery 4 ON, and charging of the lead-acid battery 4 begins (step S24).

[0038] In step S23, if the determination is made that the lithium-ion battery 3 is in the discharge phase (YES) (this does not usually occur when the Li voltage exceeds the upper limit during discharge), charging of the lead-acid battery 4 is not started, and the process proceeds to step S2.

[0039] Next, the Pb discharge ON flag is set to ON "1" (step S25). Note that the Pb discharge ON flag is set to "1" only in step S25; from step S25 onward, once the lead-acid battery 4's pre-sunset Pb charging (Figure 6, 8)) is complete, the process transitions to Pb sunset discharge (Figure 6, 9)) and sets the Pb discharge ON flag.

[0040] Subsequently, a timer for a seventh predetermined time, for example, 1 second, is activated (step S26). Next, it is determined whether the lead-acid battery 4 is discharging (step S27). If it is determined in step S27 that the lead-acid battery 4 is not discharging (charging) (NO), the process returns to step S26, and charging of the lead-acid battery 4 continues. In short, steps S26 and S27 maintain the connection to the lead-acid battery 4 as long as the controller 7 maintains charging (until sunset), and when the lighting is started by the control of the controller 7, step S27 LD The terminal signal indicates that lead-acid battery 4 is discharging (YES), and charging of lead-acid battery 4 is completed before returning to step S2.

[0041] In step S22, if the voltage of the lithium-ion battery 3 does not exceed the voltage when fully charged (NO), it is determined whether the voltage of the lithium-ion battery 3 has fallen below a predetermined voltage (lower limit voltage) (step S28). In step S28, if the voltage of the lithium-ion battery 3 exceeds the lower limit voltage (YES), it is determined whether the lithium-ion battery 3 is in the discharge phase (step S29). If the lithium-ion battery 3 is in the discharge phase (step S29:YES), the switch 9 is operated to connect to AC, turning the lithium-ion battery 3 OFF and the lead-acid battery 4 ON, and discharge by the lead-acid battery 4 is continued (step S30). After this, the Pb charging ON flag is set to ON "1" (step S38). At this time, it is determined whether the lead-acid battery 4 is in the discharge phase by the LD terminal signal (step S31), and if the lead-acid battery 4 is in the discharge phase (step S31:YES), the 8th predetermined time, for example 1 second timer is started (step S32).

[0042] Then, if the lithium-ion battery 3 is not discharging (is charging) in step S29 (NO), and if the lead-acid battery 4 is not discharging (is charging) in step 31 (NO), the process returns to step S2.

[0043] On the other hand, if the determination in step S28 indicates that the discharge voltage of the lithium-ion battery 3 does not exceed the lower limit voltage (NO), the duty cycle of the lighting output in the LED lighting device 5 is measured and the measured duty cycle is saved (step S33). This duty cycle is measured using the duty cycle measurement circuit 10 shown in Figure 5. This duty cycle measurement circuit 10 consists of a capacitor 12 (e.g., 10 μF) and a first resistor 13 (e.g., 22 kΩ) connected in parallel, with a second resistor 14 (e.g., 100 kΩ) connected in series with these capacitor 12 and first resistor 13. In short, the duty cycle measurement circuit 10 outputs a DC voltage proportional to the duty cycle of the lighting output in the LED lighting device 5, and this DC voltage is measured and saved.

[0044] In the controller 8, the DC voltage is measured after being attenuated to approximately 1 / 6 and then averaged. This DC voltage is, for example, 2.16V (={12V·22 / (100+22)}·1.0) when the duty cycle of the lighting output of the LED lighting device 5 is 100%. When the duty cycle of the lighting output of the LED lighting device 5 is 50%, it is, for example, 1.08V (={12V·22 / (100+22)}·0.5). Furthermore, if a one-chip microcontroller is used as the controller 8, the DC voltage can be measured using the built-in A / D converter (not shown). When the duty cycle of the lighting output of the LED lighting device 5 is 0 "zero", the lighting output is 0 "zero", and the controller 7 determines that the discharge has ended and the control has moved to charging.

[0045] Next, it is determined whether the lithium-ion battery 3 is discharging (step S34). If it is determined in step S34 that the lithium-ion battery 3 is discharging (YES), the counter that counts the number of loops is incremented by "+1" (step S35). In short, step S35 increments the counter by "+1" each time the loop is completed. On the other hand, if it is determined in step S34 that the lithium-ion battery 3 is not discharging (NO), the counter is reset to 0 "zero" (step S39), and the process returns to step S2.

[0046] Next, it is determined whether the counter's count (counting result) has reached the existing target number of loops LC (step S36). If it is determined in step S36 that the counter's count has reached LC (YES), then the discharge time of the lithium-ion battery 3 has elapsed (finished) for a predetermined time (predetermined number of times). For this reason, the counter's count is preset to "LC-1" (so that the counting loop can be completed only once), and the process returns to step S30. Discharge from there begins with the lead-acid battery 4, and the discharge of the lead-acid battery 4 continues in steps S30, S38, S31, and S32. If it is determined in step S31 that the lead-acid battery 4 is not discharging (is charging) (NO), the process returns to step S2. Also, if the counter's count has not reached the target number of loops LC (step S36: NO), the Pb charging ON flag is set to ON "1" (step S40), and the process returns to step S2. In addition, in step S38, the Pb charging ON flag is set to ON "1", so that when charging is initiated, 165 minutes of Pb sunrise charging (Figure 6, 5)) is always performed.

[0047] <Circuit Configuration> Next, regarding the circuit diagram of the battery control unit 6, Figure 5 This will be explained by referring to [reference]. In this embodiment, a one-chip microcontroller is used in the controller 8 as described above. The switch 9 is composed of P-type first to fourth MOSFETs 12 to 15, with the first and second MOSFETs 12 and 13 switching the lithium-ion battery 3 ON-OFF (connection to and disconnection from the controller 7), and the third and fourth MOSFETs 14 and 15 switching the lead-acid battery 4 ON-OFF. Two MOSFETs each are used for the lithium-ion battery 3 and the lead-acid battery 4 in order to disable the diodes (body diodes, parasitic diodes) formed between the internal DS of the FETs.

[0048] Furthermore, an identification LED 16 is connected to the first MOSFET 12. The identification LED 16 lights up when the lithium-ion battery 3 is ON and the lead-acid battery 4 is OFF (lithium-ion battery mode), and turns off when the lithium-ion battery 3 is OFF and the lead-acid battery 4 is ON (lead-acid battery mode), allowing the operating status to be identified. Voltage measurement when the lithium-ion battery 3 is ON is performed at the AN2 terminal, which is the A / D converter of the controller 8. In addition, a duty cycle measurement circuit 10 for measuring the duty cycle and first and second switches 17 and 18 connected to the controller 8 are provided. The first and second switches 17 and 18 allow selection of four types of load. The upper and lower voltage limits of the lithium-ion battery 3 are set to appropriate values ​​in the controller 8's program.

[0049] <Operation Timing> Next, an example of the timing of the control operations performed by the controller 8 will be explained based on Figure 6.

[0050] First, the diagram 6 The operation timings shown are based on the following assumptions: The determination of "3) Sunrise / Sunset (sunrise and sunset)" is made by the controller 7, which performs charge and discharge control, based on "2) Solar power generation voltage (voltage generated by solar panel 2)". The period after sunrise is defined as the "charging period," and the period after sunset is defined as the "discharging period." The controller 8 determines whether there is a lighting output to the LED lighting device 5 (it is determined to be discharging when the duty cycle is 20% or more, i.e., when the average voltage is 1 / 5 or more, and it is determined to be charging when the duty cycle is less than 20%). The controller 7 controls the lighting time and brightness (defined by the duty cycle) of the LED lighting device 5. The controller 8 measures the average voltage of the lighting output of the LED lighting device 5 and determines the current duty cycle (what percentage). The load on the fourth day (load from LED lighting device 5) is assumed to have increased by 31% compared to the load on the first to third days. • "5) Pb sunrise charging (charging of lead-acid battery 4 at sunrise: short-term Pb charging)", "6) Li charging (charging of lithium-ion battery 3: long-term Li charging)", and "12) Li discharge (discharging of lithium-ion battery 3: long-term Li discharge)" are performed every day without fail.

[0051] First, "5) Pb sunrise charging" is started as a charging period along with the determination of sunrise (arrows 1, 13, 26, 34). This "5) Pb sunrise charging" is performed every day during the twilight hours immediately after sunrise in order to maintain the charge state of the lead-acid battery 4.

[0052] Next, "5) Pb sunrise charging" is performed for a predetermined time, for example, 165 minutes, and then the process moves to "6) Li charging" (arrows 2, 14, 27, 35). This predetermined time is determined based on a predetermined amount of charge of the rated capacity of the lead-acid battery 4, for example, about 5%. In "5) Pb sunrise charging," the amount of power generated by the solar panel 2 is small and the charging time is short, so the lead-acid battery 4 cannot be fully charged. However, in order not to interfere with the charging of the lithium-ion battery 3 which is primarily used, the process is terminated after a predetermined time and "6) Li charging" is started.

[0053] During "6) Li-charging," the output voltage of the lithium-ion battery 3 is monitored, and when this output voltage exceeds a predetermined upper limit (YES: nearly fully charged) (arrows 3, 15, 36), "6) Li-charging" is terminated (arrows 4, 16, 37). In short, "6) Li-charging" is performed from the time when the solar panel 2 is able to generate sufficient power until the lithium-ion battery 3 is nearly fully charged.

[0054] After that, "8) Pb pre-sunset charging (charging lead-acid battery 4 before sunset: long-term Pb charging)" is started (arrows 5, 17, 38). Then, when sunset arrives, "8) Pb pre-sunset charging" is stopped.

[0055] On the other hand, if it is not "7) Li voltage exceeds upper limit (the charging voltage of lithium-ion battery 3 has exceeded the upper limit voltage)" (NO), then, for example, because lithium-ion battery 3 has not been fully charged due to the effects of rain, etc., "6) Li charging" is continued and "8) Pb charging before sunset" is not performed. In short, since lead-acid battery 4 is used secondarily, charging of lead-acid battery 4 is carried out in a manner that does not interfere with the charging of lithium-ion battery 3, which is used primarily.

[0056] Furthermore, the charging of lead-acid battery 4 by "5) Pb sunrise charging" and "8) Pb pre-sunset charging" is performed to the extent that it maintains a full charge of lead-acid battery 4.

[0057] If sunset is detected, either "6) Li charging" or "8) Pb pre-sunset charging" will be terminated (arrows 6, 18, 28, 39).

[0058] On the other hand, when "8) Pb pre-sunset charging" is started, after "8) Pb pre-sunset charging" is completed, "9) Pb sunset discharge (discharge of lead-acid battery 4 after sunset: Pb short-term discharge)" is performed for a predetermined time, for example, 0.5 hours (30 minutes) (arrows 7, 19, 40). The duration of "9) Pb sunset discharge" is calculated by determining the discharge power (unit: Ah) from the current flowing through the LED lighting device 5 and the discharge time of the lead-acid battery 4, and is set to approximately 2% of the rated capacity (unit: Ah) of the lead-acid battery 4.

[0059] After the completion of "9) Pb Sunset Discharge," the output voltage (Pb voltage) of the lead-acid battery 4 is measured. If this output voltage exceeds a predetermined standard value, in other words, if it is almost fully charged (YES: arrows 9, 42, 8, 41), then "11) Pb Extended Discharge (Extended Discharge of Lead-Acid Battery 4)" is performed for a predetermined time, for example 90 minutes (arrows 10, 43), in order to eliminate overcharging of the lead-acid battery 4 and balance the charge and discharge of the lead-acid battery 4. This predetermined time is based on a discharge amount of approximately 6% of the rated capacity of the lead-acid battery 4.

[0060] If "10) Pb voltage exceeds the standard value (the output voltage of lead-acid battery 4 exceeds the predetermined standard value)" is not achieved (NO: arrow 20), then "12) Li discharge" is started without performing "11) Pb extended discharge" (arrow 21). In short, assuming that lead-acid battery 4 is not sufficiently charged, "11) Pb extended discharge" is not performed to avoid overusing lead-acid battery 4.

[0061] On the other hand, if "7) Li voltage exceeds upper limit" does not occur (in the case of NO), "8) Pb charging before sunset" and "9) Pb discharging after sunset" are not performed, and after sunset, "12) Li discharging" is started (arrow 29).

[0062] Then, if "13) Use 68% Li (discharge and use a predetermined capacity, for example 68%, of the rated capacity of lithium-ion battery 3 to achieve its lifespan)" is YES (arrows 22, 30, 45), then "12) Li discharge" is stopped (arrows 23, 31, 46), and "14) Pre-sunrise Pb discharge: Pre-sunrise discharge of lead-acid battery 4: Pb-assisted discharge" is started (arrows 24, 32, 47), preventing the LED lighting device 5 from failing to light up and preventing the progression of degradation (reduction in lifespan) of lithium-ion battery 3 due to over-discharge. Here, the rated capacity (unit: Ah) of lithium-ion battery 3 is determined by calculating the discharge power (unit: Ah) based on the current value flowed from lithium-ion battery 3 to LED lighting device 5 and the discharge elapsed time, and considering Figure 3.

[0063] If sunrise is detected, terminate either "12) Li discharge" or "14), 16) Pb pre-sunrise discharge" (arrows 12, 25, 33, 51, 52).

[0064] Then, when "15) Li battery lower limit exceeded: the output voltage of lithium-ion battery 3 is measured and this measured output voltage falls below a predetermined lower limit" occurs (arrow 48), "12) Li discharge" is stopped (arrow 49), and "16) Pb pre-sunrise discharge: pre-sunrise discharge of lead-acid battery 4" is started (arrow 50) to protect lithium-ion battery 3 from over-discharge. This "lower limit" is, for example, the voltage (lower limit voltage) when the remaining charge of lithium-ion battery 3 is 10%. Also, "16) Pb pre-sunrise discharge" is performed so as not to exceed a predetermined discharge depth of lead-acid battery 4 (for example, 15%).

[0065] As described above, the controller 8 controls the lithium-ion battery 3 and the lead-acid battery 4 so that they do not discharge (turn on output) or stop (turn off output) simultaneously. Furthermore, when discharge begins after sunset, the Pb sunset discharge (for example, for about 30 minutes) is initiated only if the charging voltage of the lithium-ion battery 3 exceeds the upper limit voltage and Pb pre-sunset charging has occurred, after which the discharge of the lithium-ion battery 3 begins. Even if the lithium-ion battery 3 has consumed 68% of its rated capacity, if the predetermined discharge time set by the controller 7 has not ended, the lead-acid battery 4 is discharged again, thereby allowing the LED lighting device 5 to remain lit for the entire period from sunset to sunrise.

[0066] On the other hand, during charging, charging of the lead-acid battery 4 begins first (for example, for 165 minutes), followed by charging of the lithium-ion battery 3. When the lithium-ion battery 3 is fully charged, charging of the lead-acid battery 4 begins again, ensuring that either the lithium-ion battery 3 or the lead-acid battery 4 is charged throughout the entire period from sunrise to sunset. However, if the lithium-ion battery 3 cannot be fully charged due to factors such as bad weather, the lead-acid battery 4 is not recharged, and priority is given to charging the lithium-ion battery 3, which is the primary battery used.

[0067] In short, regardless of the weather conditions, the lead-acid battery 4 is always charged by the sun (for example, for 165 minutes), but the lithium-ion battery 3 is used preferentially, so the configuration ensures that the lithium-ion battery 3 is fully charged and discharged. In other words, by performing small but reliable charging and discharging of the lead-acid battery 4 in this way, its lifespan can be extended when the lead-acid battery 4 is used cyclically.

[0068] Furthermore, if the lead-acid battery 4 is deemed to have remaining charge after the Pb sunset discharge (30 minutes), an extended Pb discharge (90 minutes) is performed to reduce overcharging of the lead-acid battery 4 and prevent corrosion of the positive electrode terminal of the lead-acid battery 4, which is said to be caused by overcharging. In addition, to reduce corrosion of the negative electrode terminal, which is said to be caused by over-discharge, the Pb sunset discharge is performed only when Pb pre-sunset charging is carried out, thereby reducing over-discharge and suppressing a decrease in lifespan.

[0069] <Effects and Effects> In conventional solar lighting systems, the solar panels generate current during the day to charge a secondary battery, and the discharge current from the secondary battery powers the LED lighting at night. A controller 7 controls these currents. The secondary battery is often a single or multiple identical batteries connected in parallel. Lithium-ion batteries and lead-acid batteries are commonly used as these types of batteries capable of repeated charging and discharging. Lead-acid batteries have significant drawbacks, including their bulky shape, high weight, and a large decrease in charging capacity with repeated charging and discharging (short battery life: typically around 5 years). On the other hand, lithium-ion batteries have a long battery life (3 to 5 times longer than lead-acid batteries), but are generally much more expensive (e.g., 3.9 times more), making them costly even considering their longer lifespan. For these reasons, it is conceivable to use these different types of secondary batteries—specifically lithium-ion batteries and lead-acid batteries—in combination. Lithium-ion batteries could be used primarily to prioritize battery life, while lead-acid batteries could be used as a supplementary or backup (secondary) solution.

[0070] Generally, to extend the battery life of secondary batteries such as lithium-ion batteries and lead-acid batteries, it is considered desirable to repeatedly charge and discharge them with a small current, rather than continuously charging or discharging them. In short, alternating charge and discharge operations can suppress the deterioration of the positive or negative electrode that can occur when these secondary batteries are continuously charged or discharged.

[0071] Therefore, in this embodiment, while primarily using the lithium-ion battery 3 and secondarily using the lead-acid battery 4, the aim is to extend the battery life of both the lithium-ion battery 3 and the lead-acid battery 4 by not continuously charging or discharging them for extended periods.

[0072] Specifically, in this embodiment, the solar lighting system (secondary battery system) 1 comprises a solar panel (power generation unit) 2 that generates electricity from solar energy, secondary batteries 3 and 4 that charge the electricity generated by the solar panel 2, an LED lighting device (drive unit) 5 that is driven by the electricity charged by the secondary batteries 3 and 4, and an overall controller 10 connected to the solar panel 2, secondary batteries 3 and 4, and the LED lighting device 5, respectively, which performs charge and discharge control for the secondary batteries 3 and 4 and power supply control for the LED lighting device 5. The secondary batteries 3 and 4 consist of a lithium-ion battery (first secondary battery) 3 used primarily and a lead-acid battery (secondary secondary battery) 4 used secondarily, which has a greater decrease in charge capacity due to repeated charge and discharge compared to the lithium-ion battery 3. The overall controller 10 is configured to prioritize charging the lithium-ion battery 3 over charging the lead-acid battery 4, and to prioritize discharging the lithium-ion battery 3 over discharging the lead-acid battery 4.

[0073] This allows the charging and discharging of the lithium-ion battery 3, which is primarily used, to be prioritized over the charging and discharging of the lead-acid battery 4, thereby appropriately suppressing the decrease in the charging capacity of the lead-acid battery 4 due to repeated charging and discharging. Therefore, by using a capacity and number of lead-acid batteries 4 that can cover the shortfall until the lithium-ion battery 3 reaches its target lifespan, and by selecting the capacity and number of lithium-ion batteries 3 and lead-acid batteries 4 in the most cost-effective way while ensuring the target lifespan of the lithium-ion battery 3, the desired replacement interval (target lifespan) can be extended, and costs can be reduced.

[0074] Furthermore, the overall controller 10 controls the charging and discharging of the lithium-ion battery 3 to be longer than the charging time of the lead-acid battery 4, and also longer than the discharge time of the lead-acid battery 4 (the charge and discharge amount of the lead-acid battery 4 is approximately 20% of that of the lithium-ion battery 3), thereby more effectively suppressing the decrease in the charging capacity of the lead-acid battery 4 due to repeated charging and discharging.

[0075] Furthermore, the overall controller 10 controls the charging time of the lithium-ion battery 3 to include noon, and the charging time of the lead-acid battery 4 to be at least one of the times before or after the charging time of the lithium-ion battery 3. At the same time, the overall controller 10 is configured to control the discharge time of the lithium-ion battery 3 to include midnight, and the discharge time of the lead-acid battery 4 to be one of the times before or after the discharge time of the lithium-ion battery 3.

[0076] This allows the lithium-ion battery 3, which has a relatively large charge / discharge capacity and is primarily used, to be charged preferentially over the lead-acid battery 4 at a time when charging efficiency is relatively good, and allows the lithium-ion battery 3 to discharge for an average of about four times longer than the lead-acid battery 4. On the other hand, the lead-acid battery, which has a large degradation in charge / discharge capacity due to repeated charging and discharging, is intended to be used only as a secondary battery, and is charged before and after charging the lithium-ion battery 3, and before and after discharging the lithium-ion battery 3. This ensures that the charge amount of the lithium-ion battery 3, which is primarily used, is reliably secured while also ensuring the charge amount of the lead-acid battery 4.

[0077] As described above, in the solar lighting system 1 according to the present invention, the lithium-ion battery 3 is the primary power source, accounting for approximately 80% of charge-discharge operations (on an annual average), while the lead-acid battery 4 is secondary, accounting for the remaining approximately 20%. However, this ratio applies mostly when the weather is favorable and there is a certain amount of sunshine. In the event of adverse weather conditions such as prolonged rain during the rainy season, autumn rains, or typhoons, the roles are reversed, with the lithium-ion battery 3 providing lighting for about one night, and the system then relying on the charging capacity of the lead-acid battery 4. Therefore, it is necessary to keep the charging capacity of the lead-acid battery 4 high (close to its rated capacity) under normal circumstances, and the required rated capacity of the lead-acid battery 4 is also determined by how many days of lighting need to be maintained as a backup during adverse weather conditions.

[0078] Specifically, the overall controller 10 uses a lithium-ion battery 3 as its primary secondary battery, and since the depth of discharge of this lithium-ion battery 3 is kept to 68%, the target lifespan of 10 years can be achieved based on the cycle life characteristics of the lithium-ion battery 3. On the other hand, a lead-acid battery 4 is used as a secondary secondary battery, and the lead-acid battery 4 is not continuously charged or discharged, but rather subjected to relatively light charging and discharging (about 5-10% of the rated capacity) on a daily basis, such as charging at sunrise or before sunset. As a result, the target lifespan of 10 years can also be achieved for the lead-acid battery 4 based on its cycle life characteristics (15% of the rated capacity is the limit, as shown in Figure 4). In short, compared to achieving a target lifespan of 10 years by using multiple relatively expensive lithium-ion batteries 3, by using relatively inexpensive lead-acid batteries 4 and lithium-ion batteries 3 respectively, and by charging and discharging them within the cycle life characteristics of these lithium-ion batteries 3 and lead-acid batteries 4, the target lifespan of 10 years for these lithium-ion batteries 3 and lead-acid batteries 4 can be achieved, doubling the replacement cycle period, and thus significantly reducing the total cost of the solar lighting system 1, including operational costs. [Industrial applicability]

[0079] This invention can be used in a secondary battery system that includes a secondary battery, when two types of secondary batteries with different rates of reduced charge capacity due to repeated charging and discharging are used in combination. [Explanation of Symbols]

[0080] 1. Solar lighting system 2 Solar Panels 3. Lithium-ion battery 4 Lead-acid batteries 5 LED lighting device 6. Battery Control Unit 7 Controllers 8. Controller 9 switches

Claims

1. The power generation unit generates electricity by receiving solar energy, A secondary battery that charges the electricity generated by the aforementioned power generation unit, A drive unit that operates using electricity charged by the aforementioned secondary battery as a power source, The system includes a controller connected to the power generation unit, the secondary battery, and the drive unit, which controls the charging and discharging of the secondary battery and the power supply to the drive unit, The aforementioned secondary battery comprises a first secondary battery and a second secondary battery that exhibits a greater decrease in charging capacity due to repeated charging and discharging compared to the first secondary battery. The aforementioned controller, After sunrise, the second secondary battery is charged to 5% of its rated capacity, and then the first secondary battery is charged to full capacity. Only when the first secondary battery is fully charged, the second secondary battery is charged again before sunset. If the second secondary battery is recharged before sunset, after sunset the second secondary battery is discharged to 2% of its rated capacity, and then the first secondary battery is discharged. After the discharge of the secondary battery following sunset, the charge level of this secondary battery is measured, and if this secondary battery is nearly fully charged, it is discharged to a further 6% of its rated capacity. A secondary battery-powered system characterized by the following:

2. The controller makes the charging time of the first secondary battery longer than the charging time of the second secondary battery, and the discharge time of the first secondary battery longer than the discharge time of the second secondary battery. A secondary battery usage system according to claim 1, characterized in that...

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