DC power supply and secondary battery charging method

Abstract

To charge optimally using any natural energy power generation device.SOLUTION: A DC power supply 10 comprising a power circuit 2 to which the generated power from a natural energy power generation device 1 is supplied, and a secondary battery 4 charged by an output DC voltage Vout from the power circuit 2, wherein the power circuit 2 has a setting terminal for changing an operating point of the natural energy power generation device 1, and comprises a setting voltage change circuit 5 for changing a voltage Vset at the setting terminal so that an output power (output voltage Vout×output current Iout) of the power circuit 2 becomes maximum.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a DC power supply device and a secondary battery charging method that charges a secondary battery with power generated by natural energy generation such as solar power generation or thermoelectric power generation and supplies the charged power to a load. [Background technology]

[0002] There is known a DC power supply device that stores power generated by natural energy generation such as solar power generation in a secondary battery and supplies the stored power to a load. For example, Patent Document 1 discloses a power supply device that periodically measures the no-load open-circuit voltage of a solar cell, sets a set voltage that is a predetermined percentage (e.g., 80%) of the no-load open-circuit voltage as the maximum power point voltage, and performs maximum power point tracking control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-151857 A (claims 1 and 2) Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in Patent Document 1 is compatible with solar cells, and the set voltage is set to 80% of the no-load open-circuit voltage. However, natural energy power generation does not only include solar power generation, but also thermoelectric power generation. For thermoelectric power generation, the set voltage of 80% of the no-load open-circuit voltage is not necessarily appropriate.

[0005] The present invention has been made to solve these problems, and aims to provide a DC power supply device and a secondary battery charging method that can be suitably charged by any natural energy power generation device. [Means for solving the problem]

[0006] To achieve the above object, a first invention is a DC power supply device (10) including a power supply circuit (2) to which power generated by a natural energy power generation device (1) is supplied, and a secondary battery (4) charged with the output DC voltage of the power supply circuit, wherein the power supply circuit has a setting terminal for changing the operating point of the natural energy power generation device, and includes a set voltage change circuit (5) for changing the voltage (Vset) of the setting terminal so that the output power (output voltage Vout x output current Iout) of the power supply circuit is maximized. Note that the symbols and letters in parentheses are symbols and the like used in the embodiment and do not limit the present invention.

[0007] The second invention is a secondary battery charging method having a setting terminal for changing the operating point of a natural energy power generation device (1), in which a power supply circuit (2) supplied with power generated by the natural energy power generation device charges a secondary battery (4), characterized in that the voltage (Vset) of the setting terminal is changed so that the output power (output voltage Vout x output current Iout) of the power supply circuit is maximized. Note that the symbols and letters in parentheses are symbols etc. added in the embodiment and do not limit the present invention. [Effects of the Invention]

[0008] According to the present invention, charging can be suitably performed using any natural energy power generation device. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a configuration diagram of a natural energy storage device according to a first embodiment of the present invention. [Figure 2] 1 is a characteristic diagram showing the relationship between the illuminance received by a solar cell and the generated voltage. [Figure 3] 3 is a flowchart illustrating the operation of the natural energy storage device according to the first embodiment of the present invention. [Figure 4] FIG. 10 is a configuration diagram of a natural energy storage device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that each drawing is merely a schematic illustration to allow a sufficient understanding of the embodiments. In addition, common or similar components in each drawing are designated by the same reference numerals, and redundant explanations thereof will be omitted.

[0011] (First embodiment) FIG. 1 is a configuration diagram of a natural energy storage device according to a first embodiment of the present invention. The natural energy storage system 100 includes a natural energy power generation device 1 and a DC power supply device 10, and supplies DC power to a load via a secondary battery 4. The DC power supply device 10 includes a power supply circuit 2a, a current sensor 3, the secondary battery 4, and a set voltage changing circuit 5. The power supply circuit 2b will be described in the second embodiment.

[0012] The natural energy power generation device 1 is a power generation device that uses photovoltaic power generation, thermoelectric power generation, or the like. Photovoltaic power generation devices have the characteristic that the generated voltage drops when an output current flows due to the presence of internal resistance. In other words, a photovoltaic power generation device has a specific voltage and current (operating point) at which it can output maximum power. Furthermore, the voltage and current of this maximum power (maximum power point) varies depending on the illuminance received by the solar cell. In the case of photovoltaic power generation, the voltage at this maximum power point tends to be about 80% of the no-load open-circuit voltage. In the case of thermoelectric power generation, the voltage at the maximum power point is about 50% of the no-load open-circuit voltage.

[0013] FIG. 2 is an example of a characteristic diagram showing the relationship between the illuminance received by a solar cell and the generated voltage. The horizontal axis is illuminance [Lx] and the vertical axis is generated voltage [V]. The solid line indicates the generated voltage [V] when there is no load, and the dashed line indicates 80% of the no-load open-circuit voltage [V]. The dashed-dotted line indicates the generated voltage [V] that results in maximum output when combined with power supply circuit 2a. When the illuminance is low, the generated voltage at maximum output is 80% of the no-load open-circuit voltage [V], but as the illuminance increases, the generated voltage drops to 61% of the no-load open-circuit voltage.

[0014] Returning to the explanation of Figure 1, the power supply circuit 2a has an IN terminal (input terminal), an OUT terminal (output terminal), and a setting terminal. The natural energy power generation device 1 is connected to the IN terminal, and when the generated voltage is equal to the input voltage Vin, an input current Iin flows. The power supply circuit 2a has a built-in step-up / step-down circuit (not shown), which steps up or down the input voltage Vin and outputs the output voltage Vout to the OUT terminal.

[0015] A secondary battery 4 and a load are connected to the OUT terminal. The secondary battery 4 is charged at a fixed voltage, the output voltage Vout. A current sensor 3 is also provided at the OUT terminal to measure the output current Iout (measured current), which is the sum of the charging current flowing through the secondary battery 4 and the load current flowing through the load. If the power conversion efficiency of the power supply circuit 2a is η, then the input power (generated power) is approximately equal to the value obtained by multiplying the output power (load power) by η. In other words, Vin × Iin ≒ η × Vout × Iout.

[0016] A setting terminal voltage Vset is applied to the setting terminal, which controls the operating point (input voltage Vin, input current Iin) of the renewable energy power generation device 1 connected to the IN terminal. This control also changes the operating point. Specifically, the power supply circuit 2a periodically (periodically) opens the IN terminal and measures the no-load open-circuit voltage Vop of the solar cell serving as the renewable energy power generation device 1 via the setting terminal. Outside of the periodic measurements, the power supply circuit 2a maintains the setting terminal voltage Vset and controls the input voltage Vin to be equal to the no-load open-circuit voltage Vop multiplied by the resistor voltage divider ratio at the setting terminal. In other words, the operating point is changed. By setting the resistor voltage divider ratio to a predetermined value (e.g., approximately 80%), the solar cell operates near the maximum power point. Here, the resistor voltage divider ratio is the ratio of the parallel resistance (R2 / / R3 / / ··· / / RN) between the ground terminal and the setting terminal to the series resistance (R1+R2 / / R3 / / ··· / / RN) between the IN terminal and the ground terminal.

[0017] The secondary battery 4 is, for example, a nickel-metal hydride battery or a lithium-ion battery. A nickel-metal hydride battery is a series-parallel connection of single cells with a nominal voltage of 1.2 V. Since the charging current of the secondary battery 4 is limited, a current limiting circuit is provided at the OUT terminal of the power supply circuit 2a.

[0018] The set voltage changing circuit 5 is a voltage dividing circuit that divides the input voltage Vin and includes a plurality of (two) resistors 11 and 12, a plurality of switch-equipped resistors 13, 14, . . . 19, and a control unit 9. The resistors 11 and 12 are connected in series, one end of the resistor 11 is connected to the IN terminal of the power supply circuit 2a, a connection point P between the other end of the resistor 11 and one end of the resistor 12 is connected to the setting terminal, and the other end of the resistor 12 is grounded.

[0019] The switch resistors 13, 14,...19 are configured by connecting resistors 13a, 14a,...19a and switches 13b, 14b,...19b in series. One end of the switches 13b, 14b,...19b is collectively connected to a connection point P. The resistance values ​​of the resistors 11, 12, 13a, 14a,...19a may all be the same or may all be different. Alternatively, some may be the same and others may be different. For example, the resistance value of one resistor may be half the resistance value of another resistor. In particular, when all of the switches 13b, 14b,...19b are open, the set terminal voltage Vset is the divided voltage of the two resistors 11 and 12.

[0020] When the resistance value of the resistor 11 is R1 and the resistance value of the resistor 12 is R2, the set terminal voltage Vset is Vset=Vin(R2 / (R1+R2)) If Vin is the no-load open circuit voltage Vop and a set terminal voltage Vset is applied that makes the resistor voltage division ratio R2 / (R1+R2) approximately 80%, the solar cell will operate near the maximum power point.

[0021] Furthermore, if one or more of the switches 13b, 14b,..., 19b are short-circuited, the parallel resistance value (R2 / / R3 / / ... / / RN) decreases, and the resistor-divider ratio decreases. In other words, the set voltage change circuit 5 divides the input voltage Vin using resistors 11, 12 and the switchable resistor, and functions as a voltage divider circuit that can be set to one of multiple resistor-divider ratios. Therefore, even when the power generation voltage at the maximum power point of the solar cell falls below 80% of the no-load open-circuit voltage Vop (e.g., 61% when the illuminance is high in Figure 2), the maximum power point is maintained by appropriately switching the switches 13b, 14b,..., 19b ON / OFF. Furthermore, by increasing the resistor-divider ratio R2 / (R1+R2) of the resistors 11, 12 to more than 80%, the maximum power point is maintained even when the power generation voltage at the maximum power point of the solar cell is higher than 80% of the no-load open-circuit voltage Vop.

[0022] The control unit 9 is a CPU (Central Processing Unit) and realizes its functions by executing a program. The control unit 9 controls the opening / short-circuiting of multiple switches 13b, 14b, ..., 19b. The control unit 9 also measures the output current Iout of the power supply circuit 2a using a current sensor 3. When the output current Iout is low, the control unit 9 temporarily suspends control for a predetermined time (wait time), for example, to reduce the power consumption of the entire DC power supply device 10. The control unit 9 is driven using the charging voltage of the secondary battery 4.

[0023] 3 is a flowchart illustrating the operation of the natural energy storage device according to the first embodiment of the present invention. This flow is periodically started as an interrupt. The control unit 9 sets a predetermined wait time (S1) and measures the output current Iout using the current sensor 3 (S2). After the process of S2, the control unit 9 adjusts the operation interval (S3, S4, S5). That is, the control unit 9 adjusts the setting interval of the voltage division ratio of the voltage divider circuit of the set voltage change circuit 5.

[0024] Specifically, the control unit 9 determines whether the current value measured in S2 is equal to or greater than a threshold value (S3). If the current value is equal to or greater than the threshold value (YES in S3), the control unit 9 sets the wait time to the normal setting (S4). If the current value is less than the threshold value (NO in S3), the control unit 9 sets the wait time to a longer value (S5). Note that if the current value is equal to or greater than the threshold value (YES in S3), the control unit 9 may set the wait time to a longer value (S4). That is, when the output current Iout is low, the power consumption required for the control unit 9's processing may be large relative to the generated power. Therefore, the control unit 9 lengthens the wait time until the maximum power point is detected (S9 to S13). On the other hand, when the output current Iout is high, the control unit 9 shortens the selection interval of the switches 13b, 4b, . . . , 19b of the set voltage change circuit 5. Note that when S4 is executed without executing S5, the same wait time as S1 is set in S4.

[0025] After the process of S4 or S5, the control unit 9 determines whether the current value measured in S2 is approximately 0 (S6). Here, when the current value of the output current Iout is approximately 0, it means that the load current is approximately 0 and the charging current for charging the secondary battery 4 is approximately 0. If the output current Iout is not approximately 0 (NO in S6), the control unit 9 determines whether the current change width is large compared to the previous maximum power point detection (S7). Here, detecting the maximum power point means executing S9 to S13. Note that if there was no previous detection in S7, the control unit 9 immediately executes the process of S9.

[0026] If the current change width is small (NO in S7), the control unit 9 determines whether a certain time has elapsed since the previous maximum power point was detected (S8). The certain time is different from the Wait time determined in S1, S4, and S5. If the certain time has elapsed (YES in S8) or the current change width is large (YES in S7), the control unit 9 performs maximum power point detection (S9 to S13). If the certain time has elapsed (YES in S8), it is highly likely that the power generation conditions of the natural energy power generation device 1 have changed significantly, so the control unit 9 performs maximum power point detection. For simplicity, the following description will be given assuming that only switched resistors 13 and 14 are present, and switched resistors 15,...,19 are not present.

[0027] First, the control unit 9 turns off the switches 13b and 14b and measures the output current Iout (S9). After the process of S9, the control unit 9 turns on the switch 13b and turns off the switch 14b and measures the output current Iout (S10). After the process of S10, the control unit 9 turns off the switch 13b and turns on the switch 14b and measures the output current Iout (S11). After the process of S11, the control unit 9 turns on the switches 13b and 14b and measures the output current Iout (S12). After the process of S12, the control unit 9 switches the switches 13b and 14b to form a combination that maximizes the output current Iout (S13). As a result, the set terminal voltage Vset is set so that the output current Iout is maximized. Since the output voltage Vout is constant, the set terminal voltage Vset is set so that the output power (Vout × Iout) is maximized.

[0028] After the process of S13, or when a certain time has elapsed (NO in S8), or when the current value is approximately 0 (YES in S6), the control unit 9 waits for the set Wait time and returns to the process of S2. That is, when the current change width is small (NO in S7), the elapsed time is short (NO in S8), or when the output current Iout is approximately 0 (YES in S6), it is preferable to reduce the power consumption of the control unit 9. Therefore, the control unit 9 does not detect the maximum power point (S9 to S13) (NO in S8). In other words, the control unit 9 stops switching the selection of the switches 13b, 4b, ..., 19b of the set voltage change circuit 5. That is, the voltage division setting of the set voltage change circuit 5 is maintained.

[0029] As described above, the power supply circuit 2a used in the DC power supply device 10 of this embodiment has setting terminals that can control the operating point (input voltage Vin, input current Iin) of the natural energy power generation device 1. Specifically, when all of the switches 13b, 14b, . . . , 19b are in an open state, the power supply circuit 2a controls the input voltage Vin so that it becomes equal to the no-load open-circuit voltage Vop of the natural energy power generation device 1 multiplied by the resistor voltage division ratio (R2 / (R1+R2)). Incidentally, solar cells tend to reach their maximum power point when driven at a predetermined percentage (e.g., about 80%) of the no-load open-circuit voltage Vop. Therefore, if the resistance (R2 / (R1+R2)) is set to a constant percentage (e.g., 80%), the solar cell serving as the natural energy power generation device 1 will operate near its maximum power point.

[0030] However, when a solar cell and a power supply circuit 2a are combined, the maximum power point is not always 80% of the no-load open-circuit voltage Vop. Furthermore, in the case of a power generation source other than a solar cell, such as a thermoelectric generator, the maximum power point is approximately 50% of the no-load open-circuit voltage Vop. Therefore, in this embodiment, a set voltage change circuit 5 and a current sensor 3 are provided, and the divided voltage (set terminal voltage Vset) that divides the input voltage Vin is changed at an appropriate timing to maintain the maximum power point.

[0031] In this embodiment, as an appropriate timing for changing the divided voltage, the control unit 9 shortens (S4) the wait time until the maximum power point is detected (S9 to S13) when the output current Iout is large, and lengthens (S5) the wait time when the output current Iout is small. Also, when the current change width is small (NO in S7), the elapsed time is short (NO in S8), or the output current Iout is approximately 0 (YES in S6), the control unit 9 does not change the maximum power point.

[0032] (Second embodiment) The power supply circuit 2a of the first embodiment has a function to periodically measure the no-load open-circuit voltage Vop of the natural energy power generation device 1 and a function to control the power generation voltage of the natural energy power generation device 1 (input voltage Vin of the power supply circuit 2a) to a resistor voltage division ratio of the no-load open-circuit voltage Vop. Furthermore, using the set voltage change circuit 5, the power supply circuit 2a sets the set terminal voltage Vset to the power generation voltage at the maximum power point. This allows the power supply circuit 2a to drive the natural energy power generation device 1 at the maximum power point. In contrast, the power supply circuit 2b of this embodiment (FIG. 1) reduces the average inductor current flowing through a coil (not shown) that constitutes a step-up / step-down circuit, and maintains the input voltage Vin at a minimum input voltage equal to or higher than the set voltage set by resistors 11 and 12.

[0033] The configuration of the DC power supply device 10 of this embodiment is similar to that of the first embodiment (FIG. 1). However, the DC power supply device 10 includes a power supply circuit 2b instead of the power supply circuit 2a. A set terminal voltage Vset is applied to the power supply circuit 2b, and the power supply circuit 2b also changes the operating point (input voltage Vin, input current Iin) of the natural energy power generation device 1 connected to the IN terminal. However, the power supply circuit 2b has a function of reducing the average inductor current flowing through a coil (not shown) constituting a step-up / step-down circuit (not shown) in accordance with the set terminal voltage Vset. As a result, the power supply circuit 2b used in this embodiment maintains the input voltage Vin at or above the set voltage set by resistors 11 and 12. In other words, when the input voltage Vin falls below the set voltage, the operating point of the natural energy power generation device 1 is changed. As a result, the power generated by the natural energy power generation device 1 is maintained at or above a certain value.

[0034] (Third embodiment) In the first embodiment, the maximum power point is detected at an appropriate timing, but it may be determined whether or not to detect the maximum power point by detecting a change in the environment.

[0035] FIG. 4 is a configuration diagram of a natural energy storage device according to a third embodiment of the present invention. Similar to the natural energy power generation system 100 of the above embodiment, the natural energy power generation system 101 includes a natural energy power generation device 1 and a DC power supply device 10. The DC power supply device 10 includes a power supply circuit 2a, a current sensor 3, a secondary battery 4, and a set voltage changing circuit 5. However, the natural energy power generation system 1 differs in that it includes a sensor 20.

[0036] The sensor 20 is an illuminance sensor, a temperature sensor, or the like, and is connected to the control unit 9. The control unit 9 detects changes in the external environment, such as illuminance and temperature, and determines whether or not to perform the maximum power point detection (S9 to S13) of the above embodiment. Specifically, the control unit 9 repeats measurements by the sensor 20, and performs the maximum power point detection (S9 to S13) when the change in illuminance, temperature, or the like is greater than a threshold value.

[0037] (Variation) The present invention is not limited to the above-described embodiment, and various modifications are possible, for example, as follows. (1) The power supply circuit 2a of the first embodiment includes a step-up / step-down circuit (not shown), but is not designed to include a coil. However, the power supply circuit 2a may include a step-up / step-down coil like the power supply circuit 2b of the second embodiment.

[0038] (2) The power supply circuit 2a of the first embodiment controls and changes the operating point (input voltage Vin) of the natural energy power generation device 1 so that it becomes a voltage division ratio of the no-load open circuit voltage Vop. The power supply circuit 2b of the second embodiment limits the operating point (input voltage Vin) of the natural energy power generation device 1 so that it does not become equal to or lower than a predetermined voltage. In other words, when the input voltage Vin becomes less than a set voltage, the operating point of the natural energy power generation device 1 is changed. However, the power supply circuit may change the operating point by controlling the output voltage=input voltage Vin or output current=input current Iin of the natural energy power generation device 1. [Explanation of symbols]

[0039] 1. Natural energy power generation equipment 2a,2b power supply circuit 3 Current Sensor 4 Secondary battery 5. Voltage setting change circuit 9 Control Unit 10 DC power supply 11,12,13a,14a,19a resistor 13, 14, 19 Switched resistors 100,101 Natural energy storage system Vin Input voltage Vop No-load voltage Iin Input current Vset Set terminal voltage Vout Output voltage (load voltage, secondary battery voltage) Iout Output current (measured current)

Claims

1. A DC power supply device comprising a power supply circuit to which power generated by a natural energy power generation device is supplied, and a secondary battery that is charged by the output voltage of the power supply circuit, the power supply circuit has a setting terminal for changing an operating point of the natural energy power generation device, A set voltage change circuit is provided to change the voltage of the set terminal so that the output power of the power supply circuit is maximized. A DC power supply device characterized by:

2. a current sensor for detecting an output current of the power supply circuit; The set voltage change circuit changes the voltage of the set terminal so that the measured current of the current sensor becomes a maximum.

2. The DC power supply device according to claim 1.

3. The set voltage change circuit includes a voltage divider circuit that divides the input voltage of the power supply circuit using resistors and can be set to one of a plurality of voltage division ratios, and a control unit that selects the voltage division ratio of the voltage divider circuit.

2. The DC power supply device according to claim 1.

4. The control unit shortens the selection interval of the voltage divider circuit when the output current of the power supply circuit is large, and lengthens the selection interval of the voltage divider circuit when the output current of the power supply circuit is small.

4. The DC power supply device according to claim 3.

5. The control unit stops switching the selection of the voltage dividing circuit when the output current of the power supply circuit is substantially zero.

4. The DC power supply device according to claim 3.

6. The control unit is driven by the charging voltage of the secondary battery.

4. The DC power supply device according to claim 3.

7. A secondary battery charging method in which a power supply circuit having a setting terminal for changing an operating point of a natural energy power generation device and supplied with power generated by the natural energy power generation device charges a secondary battery, The voltage of the setting terminal is changed so that the output power of the power supply circuit is maximized. A secondary battery charging method comprising:

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