ELECTRICITY STORAGE DEVICE, ELECTRICITY STORAGE METHOD, AND POWER GENERATION SYSTEM

Abstract

To provide a power storage device, a power storage method, and a power generation system that increase a collection rate or a utilization rate of power generated by a power generation unit such as a photovoltaic power generation panel.SOLUTION: A power generation system includes: a power storage unit (6) that connects a series circuit of at least a first power storage device (capacitor 12) and a second power storage device (buttery 14), each having different charge / discharge characteristics, in parallel to a power generation unit (4), and stores power generated by the power generation unit; a first DC-DC converter (16) that controls a storage voltage of the power storage unit to a target value by using any one of the generated current, generated voltage, and generated power of the power generation unit; and a second DC-DC converter (18) that controls the current obtained in the second power storage device of the power storage unit, which is charged or discharged according to the generated power, to the target value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to storage of generated power from a power generation unit such as a solar power generation panel and control thereof. [Background technology]

[0002] A solar power generation system uses solar panels as the power generation element to generate electricity by receiving sunlight. The amount of generated power varies depending on the amount of solar radiation. Regarding such power generation systems, a system is known in which, when the amount of power generated by a solar panel is equal to or less than a predetermined value, the generated power output is stored in a capacitor, and the secondary battery is charged from the capacitor and output (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP2018-129980A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in a system (e.g., Patent Document 1) in which the weak current output by a solar panel is stored in a capacitor, the stored power is voltage converted by a DC-DC converter, and then charged into a secondary battery, there is an issue that the power consumption caused by the voltage conversion of the DC-DC converter reduces the recovery rate of the weak current.

[0005] When switching between an output mode in which the power generated by the photovoltaic panels is supplied to a power conditioner and a storage mode in which the generated power is stored in a capacitor, it is essential to set a circuit for switching between the two modes and a threshold value that triggers the switching. If this threshold value is set to a high level, the stored power increases, but the generated power sent to the power conditioner decreases and the burden on the storage capacitor that constitutes the storage device increases.

[0006] If the threshold is set to a low level, there is also the issue that mode switching will occur frequently in the weak current range when the amount of solar radiation received by the solar panel is unstable, such as on cloudy or rainy days, and this mode switching will increase power consumption.

[0007] When converting generated electricity in the weak current range using a power conditioner, it is necessary to consider unforeseen circumstances, such as the inability to obtain a practical power output due to power consumption in the internal circuits of the power conditioner, or the power conditioner becoming uncontrollable. These issues apply not only to solar panels, but also to power generation using renewable energy sources such as plant batteries.

[0008] In addition, solar panels are usually installed in a series-parallel configuration, but depending on the direction of the light-receiving surface of the power generation panel, the amount of sunlight received differs, resulting in different amounts of power generation. To avoid such effects, maximum power point tracking (MPPT) control is used. Moreover, MPPT control is required for each solar power generation panel, which increases the cost of the power conditioner.

[0009] The present inventors have discovered that in order to recover (store) generated power in the weak current range obtained from a power generation device such as a solar panel, it is more effective to avoid switching between storage mode and output mode using a switch or the like, and that simplification of the MPPT is essential.

[0010] Therefore, based on the above problems and findings, an object of the present disclosure is to increase the recovery rate or utilization rate of generated electricity obtained by a power generation unit such as a solar power generation panel. [Means for solving the problem]

[0011] In order to achieve the above object, according to one aspect of the power storage device of the present disclosure, at least Capacitor and secondary batterya power storage unit for storing the generated power of the power generation unit by connecting the series circuit in parallel with the power generation unit; a first DC-DC converter connected to the power generation unit and the capacitor, and configured to control a storage voltage of the power storage unit to a target value using any one of a generated current, a generated voltage, or a generated power of the power generation unit; and a second DC-DC converter connected to the secondary battery, and configured to control a current obtained by the secondary battery of the power storage unit, which is charged or discharged according to the generated power, to a target value. Equipped with The capacitor is connected between the input terminal of the first DC-DC converter and the input terminal of the second DC-DC converter. do.

[0013] In order to achieve the above object, Power storage device According to one aspect of the present invention, a series circuit of at least a capacitor and a secondary battery is connected in parallel to a power generation unit, and a power storage unit that stores the power generated by the power generation unit is connected to the power generation unit and the capacitor, a first DC-DC converter that controls a storage voltage of the power storage unit to a target value by using any one of a generated current, a generated voltage, or a generated power of the power generation unit; connected to the secondary battery, The power storage unit is configured to charge or discharge in accordance with the generated power. secondary battery and a second DC-DC converter that controls the output voltage to a target value by using a current flowing through the first DC-DC converter and an output voltage of the first DC-DC converter. The capacitor is connected between the input terminal of the first DC-DC converter and the input terminal of the second DC-DC converter.

[0014] In order to achieve the above object, Power storage device According to one aspect of the present invention, a series circuit of at least a capacitor and a secondary battery is connected in parallel with a power generation unit, and a power storage unit stores the power generated by the power generation unit; The power generating system further includes an inverter connected to the power generating unit and the power storage unit for converting the generated power into AC power and controlling the storage voltage of the power storage unit to a target value by using an output current and the storage voltage of the power storage unit. In this electricity storage device, a power supply voltage regulator connected to the secondary battery and disposed between the secondary battery and the inverter, The power storage unit is configured to charge or discharge in accordance with the generated power. secondary battery The power supply may be provided with a DC-DC converter that controls the current obtained to a target value. In this electricity storage device, the power generation unit may be a solar power generation panel.

[0015] In order to achieve the above object, according to one aspect of a power storage method of the present disclosure, a power storage unit includes at least Capacitor and secondary battery a step of connecting the series circuit in parallel with a power generation unit and storing the power generated by the power generation unit; The power generating unit and the capacitor are connected a step of a first DC-DC converter controlling a storage voltage of the power storage unit to a target value by using any one of a generated current, a generated voltage, or a generated power of the power generation unit; Connected to the secondary battery A second DC-DC converter a capacitor connected between an input terminal of the second DC-DC converter and an input terminal of the first DC-DC converter; The power storage unit is configured to charge or discharge in accordance with the generated power. secondary battery and controlling the current obtained to a target value.

[0016] In order to achieve the above object, according to one aspect of a power storage method of the present disclosure, a power storage unit includes at least Capacitor and secondary battery a step of connecting the series circuit in parallel with a power generation unit and storing the power generated by the power generation unit; The power generating unit and the capacitor are connected a step of a first DC-DC converter controlling a storage voltage of the power storage unit to a target value by using any one of a generated current, a generated voltage, or a generated power of the power generation unit; Connected to the secondary battery A second DC-DC converter a capacitor connected between an input terminal of the second DC-DC converter and an input terminal of the first DC-DC converter; The power storage unit is configured to charge or discharge in accordance with the generated power. secondary battery and controlling the output voltage to a target value by using the current flowing through the inverter and the output voltage.

[0017] In order to achieve the above object, according to one aspect of a power storage method of the present disclosure, a power storage unit includes at least Capacitor and secondary battery the step of connecting the series circuit in parallel with a power generation unit and storing the power generated by the power generation unit; the step of connecting an inverter to the power generation unit and the power storage unit and converting the power generated by the power generation unit into AC power; and the step of controlling the storage voltage of the power storage unit to a target value by the inverter using the output current of the inverter and the storage voltage of the power storage unit.

[0018] This power generation system In the above, the power generation unit may be a solar power generation panel.

[0019] In order to achieve the above object, according to one aspect of a power storage system of the present disclosure, the power storage system includes a power generation unit that generates DC power, and the power storage device.

[0021] In order to achieve the above object, Power Generation According to one aspect of the system, the power generating unit is a photovoltaic panel. Effect of the Invention

[0022] According to the present disclosure, any of the following effects can be obtained. (1) Since a series circuit including at least a first storage device and a second storage device having different charging and discharging characteristics is connected in parallel with the power generation unit, the power generated by the power generation unit, whose generated power fluctuates from weak power to normal power, can be stored and transmitted, thereby making it possible to compensate for the fluctuations in generated power with the stored power and to improve the recovery of generated power.

[0023] (2) Since the series circuit of the first storage device and the second storage device is connected in parallel with the power generation unit, during power generation, the generated power from the power generation unit is added to the storage unit, the storage unit is maintained in a floating and charged state, and weak power contained in the generated power can be recovered.

[0024] (3) Even if the energy to be converted into electricity, such as the amount of solar radiation, fluctuates, electricity can be stored continuously in response to increases or decreases in the power generated by the power generation unit. By setting a threshold for the generated power, it is possible to avoid switching losses that occur when switching between charging and not charging, thereby increasing the power recovery rate.

[0025] (4) When the generated power is low, the stored power can be output from the storage unit to the load or power grid, thereby realizing a stable power supply, including preventing malfunctions of the power conditioner, and improving the reliability of the power supply. [Brief description of the drawings]

[0026] [Figure 1] 1 is a diagram showing a power generation system according to a first embodiment; [Diagram 2] FIG. 13 is a diagram showing a power generation system according to a second embodiment. [Diagram 3] 1 is a diagram showing a power generation system according to a first embodiment. [Figure 4] 5A and 5B are diagrams showing operational waveforms during charging and discharging of a battery. [Diagram 5] 6A and 6B are diagrams showing operational waveforms when the amount of power generated by the power generating unit fluctuates. [Figure 6] FIG. 11 is a diagram showing a power generation system according to a second embodiment. [Figure 7]FIG. 11 is a diagram showing operational waveforms during load fluctuation. [Figure 8] 6A and 6B are diagrams showing operational waveforms when the amount of power generated by the power generating unit fluctuates. [Figure 9] FIG. 11 is a diagram showing a power generation system according to a third embodiment. [Figure 10] 5A and 5B are diagrams showing operational waveforms during charging and discharging of a battery. [Figure 11] 6A and 6B are diagrams showing operational waveforms when the amount of power generated by the power generating unit fluctuates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] First Embodiment Fig. 1 shows a power generation system 2 according to a first embodiment. The configuration shown in Fig. 1 is an example, and the present disclosure is not limited to such a configuration.

[0028] This power generation system 2 is an example of a power storage device that stores the power generation output, including weak power, output by the power generation unit 4, and is also an example of an interconnection system that converts the generated power into AC power and sends it to a load or a power grid.

[0029] The power generation system 2 is equipped with a power generation unit 4, a power storage unit 6, and a power conditioner 8. The power generation unit 4 includes a plurality of solar power generation panels 10-1, 10-2, ..., 10-n (hereinafter simply referred to as "solar panels 10") that are connected in series, in parallel, or in a series-parallel configuration. Each solar panel 10 generates power in response to the amount of solar radiation, and generates DC power including weak power. The power generation system 2 may use a power generation means that converts renewable energy into DC power, such as a plant battery panel, for the power generation unit 4, and is not limited to using the solar panels 10.

[0030] The power storage unit 6 is an example of the power storage device of the present disclosure. The power storage unit 6 includes a series circuit of a capacitor 12 and a battery 14, which is connected in parallel with the power generation unit 4 and stores the power generation current Ia of the power generation unit 4. The capacitor 12 is an example of a first power storage device among a first power storage device and a second power storage device having different charging and discharging characteristics. For example, an electric double layer capacitor is used for the capacitor 12. The battery 14 is an example of a second power storage device, and is an example of a secondary battery that can be repeatedly charged and discharged.

[0031] The capacitor 12, which is the first power storage device, is capable of rapid charging and discharging compared to the battery 14, which is the second power storage device, and is preferably one that has a slope-shaped charge and discharge curve, such as an electric double layer capacitor, a hybrid capacitor, and a pseudo-capacitor (redox capacitor). In an electric double layer capacitor, electrons are not exchanged between the electrode and the ions in the electrolyte (non-Faraday reaction), and charging and discharging are performed only by physical adsorption and desorption of ions. When ions are adsorbed on the electrode surface, an electric double layer is formed between the electrode and the electrolyte, and electricity is stored. In order to increase the capacity, the larger the electrode surface area, the more advantageous it is, and activated carbon with a large specific surface area is generally used as the electrode material (active material). In a hybrid capacitor, electricity is stored only by physical adsorption of ions in one electrode, for example, the positive electrode, as in an electric double layer capacitor, and electricity is stored in the other electrode, for example, the negative electrode, by the Faradaic reaction. For electrodes (e.g., positive electrodes) that store electricity only through the physical adsorption of ions, the same material (activated carbon) as that used in electric double layer capacitors is used as the electrode material (active material), while for electrodes (e.g., negative electrodes) where the Faraday reaction occurs, materials capable of intercalation, such as graphite and lithium titanate, are primarily used. Pseudocapacitor (redox capacitor) uses specific metals for the electrodes, allowing the use of redox capacitance in addition to the electric double layer.

[0032] Regarding the charge and discharge characteristics of the first and second power storage devices, "different charge and discharge characteristics" means that at least the charge time constant or the discharge time is different. In other words, the charge time constant or the discharge time, which represents the charge and discharge characteristics, may change in any manner, but the length of the charge time constant or the discharge time is different from that of the first and second power storage devices. The charging time constant of the capacitor 12 as the first power storage device is smaller than the charging time constant of the battery 14 as the second power storage device, or Capacitor 12 discharge time < Battery 14 discharge time This is in a relationship.

[0033] The power conditioner 8 includes a first DC (= direct current)-DC (= direct current) converter (hereinafter simply referred to as “DC-DC”) 16, a second DC (= direct current)-DC (= direct current) converter (hereinafter simply referred to as “DC-DC”) 18, and an inverter (hereinafter simply referred to as “INV”) 20.

[0034] The DC-DC 16 is a functional unit that receives the generated power of the power generation unit 4 and converts the generated power into DC power of a desired voltage, and includes a converter unit 16-2 and a control unit 16-4. The converter unit 16-2 converts the generated power into DC power of a desired voltage. The control unit 16-4 is an example of a voltage control unit, and controls the storage voltage of the power storage unit 6 to a target value using the storage voltage of the power storage unit 6 and the input current Id1 of the DC-DC 16. This control unit 16-4 may be configured with an analog circuit, or may be configured with a digital circuit such as a microcomputer. The storage voltage may be controlled using either the generated voltage or the generated power in addition to the generated current.

[0035] The DC-DC 18 is a functional unit that receives the power generated by the power generation unit 4 and converts the generated power into DC power of a desired voltage, and further charges and discharges the generated power to and from the power storage unit 6, and includes a converter unit 18-2 and a control unit 18-4. The converter unit 18-2 converts the generated power or the power of the power storage unit 6 into DC power of a desired voltage. The control unit 18-4 is an example of a current control unit, and controls the input current Id2 flowing through the battery 14, which is in a charging or discharging state according to the power generated by the power generation unit 4, to a target value. This control unit 18-4 may be configured with an analog circuit or a digital circuit such as a microcomputer.

[0036] The INV 20 receives DC power from the output terminal 21 of the DC-DC 16, 18 and converts this DC power into AC power similar to that of the power grid. When connected to the power grid, this AC power is supplied from the output terminal 22 to a load or the power grid.

[0037] <Storage Operation of Power Storage Unit 6 and Power Transmission> The power storage unit 6 is a series circuit of a capacitor 12 and a battery 14, and is connected in parallel to the power generation unit 4. The generated voltage Va of the power generation unit 4 is added to the series circuit of the capacitor 12 and the battery 14, and is shared by the capacitor 12 and the battery 14. With respect to the generated voltage Va of the power generation unit 4, if the charging voltage of the battery 14 is Vb and the charging voltage of the capacitor 12 is Vc, then the generated voltage Va is expressed by equation (1). Va = Vb + Vc (1) The power storage unit 6 receives the power generation voltage Va from the power generation unit 4, the battery 14 is charged to a charging voltage Vb via the capacitor 12, and the capacitor 12 is charged to a charging voltage Vc.

[0038] The power generation unit 4 and the capacitor 12 are connected to the DC-DC 16, and the battery 14 is connected to the DC-DC 18. The capacitor 12 is connected between the input terminals of the DC-DC 16 and 18. Therefore, the input terminal voltage of the DC-DC 16 is the power generation voltage Va, while the input terminal voltage of the DC-DC 18 is the charging voltage Vb. This charging voltage Vb is obtained from Equation (1) to Equation (2). Vb = Va - Vc ···(2) The input voltage of the DC-DC 16 is the power generation voltage Va from the power generation unit 4, while the input voltage of the DC-DC 18 is the charging voltage Vb. That is, this charging voltage Vb is the power storage voltage reduced by the charging voltage Vc shared by the capacitor 12 from the power generation voltage Va.

[0039] Therefore, the generated power including the weak power obtained by the power generation unit 4 flows into the power storage unit 6, that is, into the capacitor 12, flows into the battery 14 through this capacitor 12, and also flows into the DC-DC 16. The generated power flowing into the DC-DC 16 is transmitted to the INV 20 after the DC conversion of the DC-DC 16. The INV 20 converts the DC power of the DC-DC 16 and 18 into AC and supplies it to the load or the power grid.

[0040] The DD-DC 18 is interposed between the battery 14 and the INV 20, and its operation varies depending on the magnitude relationship between the generated power and the load power. When the generated power suffices the load power, the generated power is supplied to the INV 20 through the DD-DC 18. On the other hand, the surplus of the generated power with respect to the load power is supplied to the battery 14 through the DC-DC 18 and the battery 14 is charged. In contrast, when the generated power is insufficient with respect to the load power, the shortage is compensated by the stored power of the battery 14 and supplied to the INV 20.

[0041] <Control Operations of DC-DC 16 and 18> The generated current Ia of the power generation unit 4 is supplied to the DC-DC 16 and the power storage unit 6. The input current Id1 entering the DC-DC 16 is controlled by a current control function of the DC-DC 16, and the input current Id2 entering the DC-DC 18 from the battery 14 is controlled by a current control function of the DC-DC 18. In other words, the input currents Idl and Id2 are controlled independently.

[0042] a) When connected to the power grid (when connected to the grid) The generated voltage Va of the power generation unit 4 is applied to the power storage unit 6 and is controlled to a desired constant voltage by the control operation of the DC-DC converter 16. As a result, the generated current Ia of the power generation unit 4 becomes equal to the input current Id1 of the DC-DC converter 16 (Ia=Id1).

[0043] On the other hand, the input current Id2 flowing from the battery 14 to the DC-DC converter 18 is controlled to a desired value by the DC-DC converter 18 separately from the input current Id1. At this time, the input voltage Vd applied to the INV20 from the DC-DC converters 16 and 18 is controlled by the INV20 to a desired constant value.

[0044] b) When it is independent of the power grid (when it is not connected to the grid) As in the case of grid-connected system, the generated voltage Va is controlled to a desired constant value by the DC-DC 16, so that the generated current Ia of the power generating unit 4 becomes equal to the input current Id1 of the DC-DC 16.

[0045] INV20 receives the DC power output by DC-DC16, converts the DC power to AC power, and supplies it to the load. At this time, DC-DC18 controls the input voltage (grid link voltage) Vd to INV20 to a desired constant value.

[0046] If the power generated by the power generating unit 4 is greater than the load power, the surplus power is supplied from the DC-DC converter 18 to the battery 14 and stored therein. If the generated power of the power generating unit 4 is smaller than the load power, the DC-DC 18 discharges the shortage of power from the battery 14 and supplies it to the INV 20 side.

[0047] <Electricity storage process I> The control of the power generation system 2 includes a first power storage process I. The power storage process I is an example of a power storage method of the present disclosure. The power storage process I includes power storage by the power storage unit 6 (S101), voltage control by the DC-DC 16 (S102), current control by the DC-DC 18 (S103), and the like.

[0048] Storing electricity by the electricity storage unit 6 (S101): The electricity storage unit 6 has the configuration described above, and receives the electricity generated by the power generation unit 4, divides the voltage by the capacitor 12 and the battery 14, and stores the electricity.

[0049] Voltage control by DC-DC 16 (S102): The DC-DC 16 has the configuration already described, receives the generated current of the power generation unit 4, and controls the stored voltage of the power storage section 6 to a target value.

[0050] Current control by DC-DC 18 (S103): The DC-DC 18 has the configuration already described, and controls the current available to the battery 14 of the power storage section 6, which charges or discharges according to the power generated by the power generation unit 4, to a target value.

[0051] <Electric storage process II> The control of the power generation system 2 includes a second power storage process II. The power storage process II is an example of the power storage method of the present disclosure. The power storage process II includes power storage by the power storage unit 6 (S201), voltage control by the DC-DC 16 (S202), and voltage control by the DC-DC 18 (S203).

[0052] Storing electricity by the electricity storage unit 6 (S201): The electricity storage unit 6 has the configuration described above, and receives the electricity generated by the power generation unit 4, divides the voltage by the capacitor 12 and the battery 14, and stores the electricity.

[0053] Voltage control by DC-DC 16 (S202): The DC-DC 16 has the above-mentioned configuration, and controls the storage voltage of the power storage section 6 to a target value using the power generation current of the power generation unit 4.

[0054] Voltage control by DC-DC 18 (S203): The DC-DC 18 has the configuration already described, and controls its output voltage to a target value by using the current flowing through the battery 14 of the power storage unit 6, which is charged or discharged according to the power generated by the power generation unit 4, and the output voltage of the DC-DC 16.

[0055] <Advantages of the First Embodiment> According to the first embodiment, any one of the following effects can be obtained. (1) Since the power storage section 6 that stores the generated power of the power generation unit 4 is composed of a series circuit of the capacitor 12 and the battery 14, the generated voltage Va is divided into a charging voltage Vb on the battery 14 side and a charging voltage Vc on the capacitor 12 side as shown in formula (1), and this voltage sharing is satisfied with a value according to the number of each cell. As a result, the number of series-connected capacitor cells of the capacitor 12 and battery cells of the battery 14 can be reduced.

[0056] (2) The power generated by the power generation unit 4, that is, the power ranging from weak to large, can be received by the series circuit of the capacitor 12 and the battery 14 of the power storage section 6 and stored continuously and seamlessly. This operation can be realized mainly by the control operation of the DC-DC converters 16 and 18, and there is no need for a charge switching or discharge circuit that selectively charges the capacitor depending on the power. This reduces the power loss due to the charge / discharge switching, and increases the recovery rate of the generated power.

[0057] (3) Since the input control of the power generated by the power generation unit 4 is performed by the DC-DC 16, the circuit for MPPT control that was previously installed for each solar panel 10 is no longer necessary, and the cost of the power conditioner 8 can be reduced. Since the capacitor 12 is installed in the power storage unit 6, the MPPT function can be simplified, and it is sufficient to perform MPPT control on only one DC-DC 16.

[0058] (4) By the operation of the DC-DC converter 18, the surplus of generated power relative to the load power required by the load can be stored in the battery 14, and the deficiency can be supplied from the battery 14 through the INV 20 to the load.

[0059] Second Embodiment Fig. 2 shows a power generation system 2 according to a second embodiment. In Fig. 2, the same parts as those in Fig. 1 are denoted by the same reference numerals. The configuration shown in Fig. 2 is an example, and the present disclosure is not limited to such a configuration.

[0060] Similar to the first embodiment, the power generation system 2 according to the second embodiment is an example of a transmission system that receives the power generated by the power generation unit 4 as input power and transmits it to a load or a power distribution system, an example of a conversion system to AC power, or an example of a power storage device for the input power from the power generation unit 4. The power generation system 2 includes a power generation unit 4, a power storage unit 6, and a power conditioner 8. The power generation unit 4 and the power storage section 6 are similar to those in the first embodiment, and therefore the description thereof will be omitted.

[0061] The power conditioner 8 shown in Fig. 2 includes a DC-DC 18 and an INV 24. That is, the function of the DC-DC 16 in the first embodiment is realized by the INV 24. The DC-DC 18 is the same as in the first embodiment (Fig. 1), and therefore a description thereof will be omitted.

[0062] The INV 24 includes an inverter unit 24-2 and a control unit 24-4. The inverter unit 24-2 is connected to the power generation unit 4 and the power storage unit 6, receives power generated by the power generation unit 4, converts it into AC power with an AC voltage similar to commercial AC, and sends it out from the output terminal 22 to the power grid. The control unit 24-4 is an example of an inverter control unit, and is a voltage control unit that controls the storage voltage (DC link voltage Vd=input voltage) of the power storage unit 6 to a target value, and also constitutes an inverter current control unit that controls the inverter current. This control unit 24-4 may be configured with an analog circuit, or may be configured with a digital circuit such as a microcomputer.

[0063] a) When connected to the power grid (when connected to the grid) The generated voltage Va of the power generating unit 4 is applied to the power storage section 6 and is controlled to a desired constant voltage by the voltage control operation of the INV 24. As a result, the generated current Ia of the power generating unit 4 becomes equal to the input current Id1 of the INV 24 (Ia=Id1).

[0064] An input current Id2 flowing from the battery 14 to the DC-DC converter 18 is controlled by the DC-DC converter 18 to a desired value separately from the input current Id1. At this time, the input voltage Vd applied to INV24 is controlled to a desired constant value by INV24.

[0065] b) When it is independent of the power grid (when it is not connected to the grid) The INV24 receives DC power generated by the power generating unit 4, converts the DC power to AC power, and supplies it to the load. At this time, the DC-DC18 controls the input voltage Vd=Va to the INV24 to a desired constant value. As a result, the generated current Ia of the power generating unit 4 becomes equal to the input current Id1 of the INV24.

[0066] When the power generated by the power generating unit 4 is low, for example when the amount of solar radiation is low, the DC-DC converter 18 reduces the target voltage value of the input voltage Vd, and reduces the charging voltage Vc of the capacitor 12. If the generated power of the power generation unit 4 is greater than the load power, the DC-DC 18 supplies the surplus power to the battery 14 for charging. If the power generated by the power generating unit 4 is smaller than the load power, the DC-DC 18 discharges the shortage of power from the battery 14 to the INV 24 side.

[0067] <Electric storage process III> The control of the power generation system 2 includes a third power storage process III. The power storage process III is an example of the power storage method of the present disclosure. The power storage process III includes power storage by the power storage unit 6 (S301), current control by the DC-DC 18 (S302), and control by the INV 24 (S303, S304). Storage of electricity by the electricity storage unit 6 (S301): The electricity storage unit 6 has the above-mentioned configuration and stores the electricity generated by the power generation unit 4.

[0068] Current control by DC-DC 18 (S302): The DC-DC 18 has the above-mentioned configuration and controls the current available to the battery 14 of the power storage section 6, which charges or discharges according to the power generated by the power generation unit 4, to a target value.

[0069] Control by the INV 24 (S303): The INV 24 has the above-mentioned configuration and converts the power generated by the power generation unit 4 into AC power. Control by INV 24 (S304): The INV 24 has the above-described configuration, and controls the storage voltage of the power storage unit 6 to a target value using the inverter current and the storage voltage of the power storage unit 6.

[0070] <Electricity storage process IV> The control of the power generation system 2 includes a fourth power storage process IV. The power storage process IV is an example of the power storage method of the present disclosure. The power storage process IV includes power storage by the power storage unit 6 (S401), current control by the DC-DC 18 (S402), voltage control (S403), and control by the INV 24 (S404). Storage of electricity by the electricity storage unit 6 (S401): The electricity storage unit 6 has the above-mentioned configuration and stores the electricity generated by the power generation unit 4.

[0071] Current control by DC-DC 18 (S402): The DC-DC 18 has the above-mentioned configuration and controls the current available to the battery 14 of the power storage section 6, which charges or discharges according to the power generated by the power generation unit 4, to a target value.

[0072] Control by the DC-DC 18 (S403): The DC-DC 18 has the above-mentioned configuration and controls Va=Vd to a target value using the current of the battery 14. Control by the INV 24 (S404): The INV 24 has the above-mentioned configuration and converts the power generated by the power generation unit 4 into AC power.

[0073] <Advantages of the Second Embodiment> According to the second embodiment, any one of the following effects can be obtained. (1) The same effects as those of the first embodiment can be obtained without installing the DC-DC16 (FIG. 1). (2) DC-DC16 is not required, which simplifies the circuit configuration. (3) The control required by DC-DC16 is no longer necessary. (4) Since the charging voltage Vc shared by the capacitor 12 is reduced, the weak power output by the power generating unit 4 can be efficiently stored. EXAMPLES

[0074] Fig. 3 shows a power generation system 2 according to Example 1. Example 1 relates to the first embodiment and is the power generation system 2 when connected to a grid. In Fig. 3, the same parts as in Fig. 1 are denoted by the same reference numerals. In the power generation system 2 when connected to the grid, a power generation unit 4, a power storage unit 6, and DC-DCs 16 and 18 are used. As shown in Fig. 3, the DC-DC 16 includes a converter unit 16-2 and a control unit 16-4, and the DC-DC 18 includes a converter unit 18-2 and a control unit 18-4, and outputs DC power from output terminals 21-1 and 21-2.

[0075] <Power Generation Unit 4> The power generating unit 4 generates power ranging from weak power to normal power, similar to the previously described power generating unit 4. Therefore, this power generating unit 4 can be simulated by a current source whose output power is controllable.

[0076] <Storage unit 6> The power storage unit 6 uses a series circuit of a capacitor 12 and a battery 14. The battery 14 can be simulated by, for example, generating a voltage that is equivalent to the stored voltage of the battery 14 in the actual device, and using a voltage source whose current is controllable in the same way as the charge / discharge current. A voltmeter 13 and an ammeter 15 are provided next to the power storage unit 6. The voltmeter 13 measures the terminal voltage of the power storage unit 6, i.e., the stored voltage of the power storage unit 6. The ammeter 15 is connected to an input unit of the converter unit 18-2 of the DC-DC 18, and measures an input current Id2 which is a charging current or discharging current flowing to the battery 14.

[0077] <dc-dc16> The converter section 16-2 is composed of a non-isolated chopper circuit. This chopper circuit is composed of, for example, transistors 28, 30, diodes 32, 34, and a choke coil 36. The serially connected transistors 28, 30 form a switch circuit that alternately conducts current. The diode 32 forms a freewheeling diode that circulates the operating current when the transistor 28 is cut off. The diode 34 forms a freewheeling diode that circulates the operating current when the transistor 30 is cut off. The choke coil 36 is connected between the power generation unit 4 and the input section of the converter section 16-2, and holds power energy in response to the switching of the transistors 28, 30.

[0078] Control unit 16-4 controls the storage voltage of power storage unit 6 to a target value using the power generation voltage Va and input current Id1 fed back from power storage unit 6. Therefore, control unit 16-4 includes a voltage control unit 16-42 which is a voltage control system using the power generation voltage Va, and a current control unit 16-44 which is a current control system using the input current Id1. Voltage control unit 16-42 is composed of an adder 38 and a coefficient amplifier 40, and current control unit 16-44 is composed of an adder 42 and a coefficient amplifier 44.

[0079] Adder 38 is an example of a comparator that compares the stored voltage with a target voltage value. A target value of the stored voltage is set to a non-inverting input (+) of adder 38 from a voltage source 46, and the stored voltage of the storage unit 6 detected by an insulating amplifier 48 is applied to its inverting input (-). The insulating amplifier 48 is an example of a voltage detection means that detects the stored voltage of the storage unit 6. Therefore, the difference voltage between the target voltage and the stored voltage is obtained at the adder 38. For integrated control of the voltage control system and the current control system, the output of this adder 38 is multiplied by a coefficient (=K1) at the coefficient amplifier 40.

[0080] The adder 42 is an example of a comparator that compares the output of the coefficient amplifier 40 with a voltage corresponding to the input current Id1. The output of the coefficient amplifier 40 is applied to the non-inverting input (+) of the adder 42, and the detection output of the input current Id1 is applied to the inverting input (-) of the adder 42 from the Hall element 50. The Hall element 50 is connected to the input part of the converter unit 16-2, and is an example of a current detection means that detects the input current Id1. Therefore, the difference voltage between the non-inverting input (+) and the inverting input (-) is obtained at the adder 42. The output of the adder 42 is multiplied by a coefficient (=K2) at the coefficient amplifier 44, and a modulated voltage is generated from the coefficient amplifier 44.

[0081] The comparison amplifier 52 is an example of a first modulator. A triangular wave voltage is applied to the non-inverting input (+) of the comparison amplifier 52 from a triangular wave generator 56, and a modulated voltage is applied to its inverting input (-) from the coefficient amplifier 44. Therefore, in the comparison amplifier 52, the modulated voltage is modulated by the triangular wave voltage, and the modulation factor of the modulator (= comparison amplifier 52) is adjusted so that the storage voltage of the storage unit 6 coincides with the target value.

[0082] The modulated output of the comparison amplifier 52 is applied to the base of the transistor 28 via a buffer amplifier 58, and this modulated output is inverted by an inverter 60 and then applied to the base of the transistor 30 via a buffer amplifier 62. Therefore, based on the output of the comparison amplifier 52, that is, in synchronization with the triangular wave period, the transistors 28 and 30 are alternately turned on and off to turn on and off the DC output, and in combination with the smoothing function provided by the charge storage of the choke coil 36, a DC-DC16 DC output is obtained.

[0083] <dc-dc18> Converter unit 18-2 is composed of a non-insulated chopper circuit, and is composed of, for example, transistors 64, 66, diodes 68, 70, and a choke coil 72. The serially connected transistors 64, 66 constitute a switch circuit that alternately conducts. Diode 68 constitutes a freewheeling diode that circulates the operating current when transistor 64 is cut off, and diode 70 constitutes a freewheeling diode that circulates the operating current when transistor 66 is cut off. Choke coil 72 is connected between battery 14 of power storage unit 6 and the input unit of converter unit 18-2, and holds power energy in response to switching of transistors 64, 66.

[0084] Control unit 18-4 controls input current Id2 fed back from power storage unit 6 to a target current value. Therefore, control unit 18-4 is configured with a DC voltage control system circuit having a current control system based on input current Id2, and is configured with adder 74 and coefficient amplifier 76. A target value of the input current Id2 is set at the non-inverting input (+) of the adder 74 by a voltage source 78, and the detection output of the input current Id2 is applied to the inverting input (-) of the adder 74 from a Hall element 80. The Hall element 80 is connected to the input part of the converter unit 18-2, and is an example of a current detection means for detecting the input current Id2. Therefore, the difference voltage between the non-inverting input (+) and the inverting input (-) is obtained at the adder 74. The output of this adder 74 is multiplied by a coefficient (=K3) at the coefficient amplifier 76, and a modulated voltage is generated from the coefficient amplifier 76.

[0085] The comparison amplifier 54 is an example of a second modulator. A triangular wave voltage is applied to the non-inverting input (+) of the comparison amplifier 54 from the triangular wave generator 56, and a modulated voltage is applied to its inverting input (-) from the coefficient amplifier 76. Therefore, in the comparison amplifier 54, the modulated voltage is modulated by the triangular wave voltage, and the modulation rate of the modulator (= comparison amplifier 54) is adjusted by the level of the modulated voltage relative to the triangular wave voltage so that the input current Id2 coincides with the target current value.

[0086] The modulated output of the comparison amplifier 54 is applied to the base of the transistor 64 via a buffer amplifier 82, and this modulated output is inverted by an inverter 84 and then applied to the base of the transistor 66 via a buffer amplifier 86. Therefore, based on the output of the comparison amplifier 54, the transistors 64 and 66 are alternately turned on and off to turn on and off the DC output, and the current reflux by the diode 68 or the diode 70, combined with the smoothing function by the charge storage of the choke coil 72, produces a DC output of the DC-DC18.

[0087] <Example 1-1 of operation when charging and discharging battery 14> This operation example 1-1 assumes an operation during charging and discharging of the battery 14. The power generation current Ia of the power generation unit 4 is set to a constant value, for example, 10 [A].

[0088] 4A indicates the power generation voltage Va of the power generation unit 4. When the battery 14 is charged or discharged, the storage voltage is controlled to a constant voltage, for example, 250 [V], which is a target voltage defined by the voltage source 46, and at this time, the power generation current Ia of the power generation unit 4 is a constant value, for example, 10 [A].

[0089] In contrast, FIG. 4B shows the input current Id1 of the DC-DC 16 and the input current Id2 of the DC-DC 18. It can be confirmed that the input current Id1 is a constant value, Id1 = 10 [A] = Ia, as a result of voltage control and current control by the DC-DC 16. The generated current Ia flowing into the capacitor 12 is equal to the flowing out Id1, and the capacitor 12 is neither charged nor discharged. At this time, the battery 14 is charging and discharging. In the input current Id2 of the DC-DC 18, the input current Id2-1 in the discharging section of the battery 14 is Id2-1=5 [A], and the input current Id2-2 in the charging section of the battery 14 is Id2-2=-5 [A]. It can be confirmed that the control of the input current Id2 by the DC-DC 18 and the control of the generated voltage Va by the DC-DC 16 can be controlled independently without mutual interference.

[0090] <Example 1-2 of operation when the power generation amount of power generation unit 4 fluctuates> This operation example 1-2 assumes operation when the power generation amount of the power generating unit 4 fluctuates. The power generation voltage Va is controlled to a constant value, for example, Va=250 [V], for the power generated by the power generating unit 4. In this case, the power generation amount and power generation current Ia of the power generating unit 4 fluctuate greatly, for example, Ia=0 [A] to 10 [A].

[0091] A in FIG. 5 shows the generated voltage Va (the input voltage of the DC-DC 16). As the amount of power generated by the power generating unit 4 changes, the power generation current Ia fluctuates, for example, from 10 A to 0 A and from 0 A to 10 A. In this case, it can be seen that the storage voltage is controlled to a constant voltage, for example, 250 V, which is a target value, despite the fluctuation of the power generation current Ia.

[0092] FIG. 5B shows the input current Id1 of the DC-DC 16 and the input current Id2 of the DC-DC 18. The input current Id1 becomes equal to the fluctuation of the generated current Ia as a result of control of the charging voltage of the storage unit 6 by the DC-DC 16 and the input current Id1. In this input current Id1, the input current Id1-1 in the section where the generated current Ia is 10 [A] is Id1-1=10 [A], and the input current Id1-2 in the section where the generated current Ia is 0 [A] is Id1-2=0 [A]. In contrast, since the target value of the input current Id2 of the DC-DC18 is a constant value of 0 [A], it can be confirmed that it is possible to control Id2 = 0 [A]. It can be confirmed that the control of the input current Id2 by the DC-DC18 and the control of the generated voltage Va by the DC-DC16 can be controlled independently without interfering with each other.

[0093] <Effects of Example 1> According to the first embodiment, any one of the following effects can be obtained. (1) The configuration shown in the first embodiment described above can be realized, and the same effects as those of the first embodiment can be obtained. (2) By the charging and discharging operation of the power storage section 6, the weak power obtained from the power generation unit 4 can be charged into the capacitor 12, and the generated power can be recovered regardless of the magnitude of the generated power. (3) There is no need to use switches or other elements to switch between charging and discharging depending on the level of generated power. Even if the level of generated power fluctuates, the generated power can be recovered seamlessly and used effectively. EXAMPLES

[0094] Fig. 6 shows the power generation system 2 according to Example 2. Example 2 shows a simulation circuit of the power generation system 2 according to the first embodiment, which is independent from the grid. In Fig. 6, the same parts as those in Figs. 1 and 3 are denoted by the same reference numerals. The power generation system 2 shown in FIG. 6 includes a battery 14, a power storage unit 6, and DC-DC converters 16 and 18 in a power conditioner 8.

[0095] <Battery 14> The battery 14 is the same as that in the first embodiment (FIG. 3), and therefore a description thereof will be omitted.

[0096] <Storage unit 6> The power storage unit 6 is the same as that in the first embodiment (FIG. 3), and therefore a description thereof will be omitted.

[0097] <Power conditioner 8> The power conditioner 8 includes a capacitor 88 as well as DC-DC converters 16 and 18, and outputs DC power from output terminals 21-1 and 21-2.

[0098] <dc-dc16> Converter section 16-2, voltage control section 16-42 of control section 16-4, and current control section 16-44 are the same as those in the first embodiment (FIG. 3), so the same reference numerals are used for the respective components and the description thereof will be omitted.

[0099] <dc-dc18> The DC-DC 18 is made up of a converter section 18-2 and a control section 18-6. Converter section 18-2 is the same as that in the first embodiment (FIG. 3), so the same reference numerals are used for the respective components and the description thereof will be omitted.

[0100] The control unit 18-6 controls the output voltage obtained on the output side of the DC-DC 18 to a target value using the input voltage Vd fed back from the output side of the DC-DC 18 and the input current Id2 fed back from the power storage unit 6. Therefore, the control unit 18-6 includes a voltage control unit 18-62 which is a voltage control system using the output voltage, and a current control unit 18-64 which is a current control system using the input current Id2. The voltage control unit 18-62 is composed of a coefficient amplifier 90 and an adder 92, and the current control unit 18-64 is composed of an adder 94 and a coefficient amplifier 96.

[0101] A voltage source 98 sets a reference voltage as a target value for the input voltage Vd. This target value is multiplied by a coefficient (=K4) in a coefficient amplifier 90. An adder 92 is an example of a comparator that compares the target value with the output voltage. The target value is set at the non-inverting input (+) of this adder 92, and the voltage across the capacitor 88, i.e., the output voltage detected by an isolation amplifier 100, is added to its inverting input (-). Thus, the adder 92 obtains a difference voltage between the target value and the output voltage.

[0102] The adder 94 is an example of a comparator that compares the output voltage of the adder 92 with a voltage representing the input current Id2. The output voltage of the adder 92 is applied to the non-inverting input (+) of this adder 94, and the detection output of the input current Id2 from the Hall element 80 described above is applied to the inverting input (-). Therefore, the difference voltage between the non-inverting input (+) and the inverting input (-) is obtained at the adder 94. The output of the adder 94 is multiplied by a coefficient (=K5) at the coefficient amplifier 96, and a modulated voltage is generated from the coefficient amplifier 96.

[0103] A triangular wave voltage is applied to the non-inverting input (+) of the comparison amplifier 54 from the triangular wave generator 56, and a modulated voltage is applied to its inverting input (-) from the coefficient amplifier 96. Therefore, in the comparison amplifier 54, the modulated voltage is modulated by the triangular wave voltage, and the modulation rate of the modulator (= comparison amplifier 54) is adjusted by the level of the modulated voltage relative to the triangular wave voltage so that the input voltage Vd coincides with the target value.

[0104] The modulated output of the comparison amplifier 54 is applied to the base of the transistor 64 via the buffer amplifier 82, and after being inverted by the inverter 84, is applied to the base of the transistor 66 via the buffer amplifier 86. Based on the modulated output of the comparison amplifier 54, the transistors 64 and 66 are alternately turned on and off to switch the DC output, and the current reflux by the diode 68 or the diode 70, coupled with the smoothing function by the charge storage of the choke coil 72, provides the DC output of the DC-DC 18. Therefore, the capacitor 88 of the power conditioner 8 obtains DC power having an input voltage Vd controlled to the target value of the voltage source 98, and the power can be taken out from the output terminals 21-1 and 21-2.

[0105] <Example 2-1 of operation during load fluctuation> This operation example 2-1 assumes operation during load fluctuation. During load fluctuation, the load current Ie, which is the operating current flowing through the load, fluctuates, for example, between 0 [A] and 15 [A], and the power generation current Ia of the power generation unit 4 is set to a constant value, for example, 10 [A]. At this time, the input voltage Vd is controlled to, for example, 380 [V]. The power generation voltage Va of the power generation unit 4 is controlled to a constant value, for example, 250 [V]. In other words, the storage voltage of the power storage unit 6 is controlled to 250 [V].

[0106] A in FIG. 7 shows the generated voltage Va and the load voltage Ve=Vd during load fluctuation. It can be confirmed that the generated voltage Va controlled by the DC-DC16 can be controlled to the target value. It can be confirmed that the load voltage Ve controlled by the DC-DC18 can be controlled to the target value, although a steady-state deviation occurs. B in FIG. 7 shows the load current Ie, the input current Id1 of the DC-DC16, and the input current Id2 of the DC-DC18. The load current Ie is varied in the range of 0 [A] to 15 [A]. Since the generated current Ia is a constant value, it can be confirmed that the input current Id1 is controlled to a constant value of 10 [A] as a result of the DC-DC16 controlling the generated voltage Va and the input current Id1. In contrast, the input current Id2 varies due to the load fluctuation. In the input current Id2, Id2-1 in the section Ie=15 [A] is the input current in the discharging section, and Id2-2 in the section Ie=0 [A] is the input current in the charging section of the battery 14.

[0107] <Example 2-2 of operation when the power generation amount of power generation unit 4 fluctuates> This operation example 2-2 assumes operation when the amount of power generated by the power generation unit 4 fluctuates. The power generation current Ia of the power generation unit 4 fluctuates between 0 [A] and 15 [A], and the load current Ie is a constant value, for example, 10 [A]. At this time, the load voltage Ve is controlled to, for example, 380 [V]. The power generation voltage Va from the power generation unit 4 is controlled to a constant value, for example, 250 [V]. In other words, the storage voltage of the storage unit 6 is controlled to 250 [V].

[0108] A in Fig. 8 shows the generated voltage Va and the load voltage Ve. It can be seen that the generated voltage Va is controlled to the target value by the DC-DC 16. It can be seen that the load voltage Ve is controlled by the DC-DC 18, although a steady-state deviation occurs. B in Fig. 8 shows the load current Ie and the input currents Id1 and Id2. The load current Ie is a constant value, for example, 10 [A]. In contrast, the input current Id1 fluctuates greatly depending on the generated current. In this input current Id1, Id1-1 is the input current in the section where the generated current is 15 [A], and Id1-2 is the input current in the section where the generated current is 0 [A]. Similarly, the input current Id2 of the DC-DC converter 18 also varies in accordance with the fluctuation in the generated power as the battery 14 is charged and discharged. In this input current Id2, Id2-1 is the input current in the range where the generated power is 15 [A], and Id2-2 is the input current in the range where the generated power is 0 [A]. It can be confirmed that the control of the input current Id2 by the DC-DC18 and the control of the generated voltage Va by the DC-DC16 can be controlled independently without interfering with each other.

[0109] <Effects of Example 2> According to the second embodiment, any one of the following effects can be obtained. (1) The configuration shown in the first embodiment described above can be realized, and the same effects as those of the first embodiment can be obtained. (2) By the same charging and discharging operation of the power storage section 6 as in the first embodiment, the weak power obtained from the power generation unit 4 can be charged into the capacitor 12, and the generated power can be recovered regardless of the magnitude of the generated power. (3) In the second embodiment as well, there is no need to use an element such as a switch to switch between charging and discharging depending on the level of generated power. Even if the level of generated power fluctuates, the generated power can be recovered seamlessly and effectively utilized. EXAMPLES

[0110] Fig. 9 shows a power generation system 2 according to Example 3. Example 3 shows a simulation circuit of the power generation system 2 according to the second embodiment, which is linked to a grid. In Fig. 9, the same parts as those in Figs. 2 and 3 are denoted by the same reference numerals. The power generation system 2 shown in FIG. 9 includes a battery 14, a power storage unit 6, and a DC-DC converter 18 and an INV 24 in a power conditioner 8.

[0111] <Battery 14> The battery 14 is the same as that in the first embodiment (FIG. 3), and therefore a description thereof will be omitted.

[0112] <Storage unit 6> The power storage unit 6 is the same as that in the first embodiment (FIG. 3), and therefore a description thereof will be omitted.

[0113] <Power conditioner 8> The power conditioner 8 includes a DC-DC converter 18 and an INV 24, and is connected to an AC power source 102. The INV 24 is an example of a connected inverter.

[0114] <dc-dc18> As in the first embodiment, the DC-DC converter 18 is made up of a non-insulated converter section 18-2 and a control section 18-4. 3, the components are given the same reference numerals and the description thereof is omitted. In the third embodiment, the non-inverting input (+) of the adder 74 is connected to a reference potential point 79 instead of the voltage source 78, so that a current of 0 [A] is set.

[0115] <inv24> The INV 24 is made up of an inverter section 24-2 and a control section 24-4. The inverter section 24-2 constitutes an inverter section linked to the power system, and includes a bridge circuit consisting of transistors 104, 106, 108, and 110 and diodes 112, 114, 116, and 118, and a choke coil 120. The transistors 104, 106 and the transistors 108 and 110 are controlled to be alternately turned on or off. The diodes 112, 114, 116, and 118 are freewheeling diodes that freewheel the operating current when the adjacent transistors 104, 106, 108, and 110 are turned off.

[0116] The control unit 24-4 includes a voltage control unit 24-42 and a current control unit 24-44. The voltage control unit 24-42 controls the DC link voltage (=load voltage) Ve, and the current control unit 24-44 controls the inverter current Iinv. The voltage control unit 24-42 is composed of an adder 122, a coefficient amplifier 124, and a multiplier 126, and the current control unit 24-44 is composed of an adder 128 and a coefficient amplifier 130.

[0117] Adder 122 is an example of a comparator that compares the storage voltage with a target value. A target value of the storage voltage is set to a non-inverting input (+) of adder 122 from voltage source 132, and the storage voltage of storage unit 6 detected by insulating amplifier 48 is added to its inverting input (-). Therefore, the output of adder 122 provides a difference voltage between the storage voltage and the target value.

[0118] The output of the adder 122 is multiplied by a coefficient (=K6) in a coefficient amplifier 124, extracted, and added to a multiplier 126. The multiplier 126 multiplies the output of the coefficient amplifier 124 by an AC voltage applied from an AC source 134 to output an AC voltage, and adds this AC voltage to an adder 128.

[0119] The adder 128 is an example of a comparator that compares the output of the multiplier 126 with the inverter current Iinv. The output of the multiplier 126 is applied to a non-inverting input (+) of the adder 128, and the detection output of the inverter current Iinv from the Hall element 136 is applied to its inverting input (-). Therefore, the difference voltage between the non-inverting input (+) and the inverting input (-) is obtained at the adder 128. The output of the adder 128 is multiplied by a coefficient (=K7) at the coefficient amplifier 130 to generate a modulated voltage.

[0120] A triangular wave voltage is applied to the non-inverting input (+) of the comparison amplifier 52 from the triangular wave generator 56, and a modulated voltage is applied to its inverting input (-) from the coefficient amplifier 130. Therefore, in the comparison amplifier 52, the modulated voltage is modulated by the triangular wave voltage, and the modulation factor of the modulator (= comparison amplifier 52) is adjusted so that the storage voltage coincides with the target value according to the inverter current Iinv and the storage voltage.

[0121] The modulated output of the comparison amplifier 52 is applied to the base of the transistor 104 via a buffer amplifier 138 and to the base of the transistor 106 via a buffer amplifier 140. This modulated output is inverted by an inverter 142 and then applied to the base of the transistor 108 via a buffer amplifier 144 and to the base of the transistor 110 via a buffer amplifier 146. Therefore, based on the output of the comparison amplifier 52, that is, in combination with the smoothing function provided by the charge storage of the choke coil 120 which alternately turns on the transistors 104, 106 and the transistors 108, 110 in synchronization with the triangular wave period, AC power is obtained and is connected to the AC power source 102.

[0122] <Operation example 3-1 when connected to the grid> This operation example 3-1 assumes operation during grid-connection. The battery 14 is in a charging / discharging state, the input current Id2 fluctuates, for example, between Id2=-5 [A] and 5 [A], and the power generation current Ia of the power generation unit 4 is a constant value, for example, Ia=10 [A].

[0123] 10A shows the generated current Ia and the input current Id2. In the input current Id2, Id2-1 represents the charging current from the battery 14, and Id2-2 represents the discharging current to the battery 14. In contrast, B in Fig. 10 shows that the voltage Vd and the load voltage Ve are Vd = Ve. Although the load voltage Ve, which is a DC voltage, has a steady-state deviation due to the voltage and current control of the inverter 24, it can be confirmed that it can be controlled to the target value. C in Fig. 10 shows the inverter current Iinv. The inverter current Iinv is an AC current output by the INV 24, and its amplitude fluctuates due to the charging and discharging of the battery 14. It can be confirmed that the amplitude of the AC current is large in the discharge section from the battery and is small in the charge section.

[0124] <Example 3-2 of operation when the power generation amount of the power generation unit 4 fluctuates> This operation example 3-2 assumes operation during fluctuations in the amount of power generated by the power generating unit 4. The power generation current Ia of the power generating unit 4 fluctuates, for example, between Ia=0 [A] and 10 [A], and the input current Id2 is a constant value, for example, Id2=0 [A].

[0125] 11A shows the generated current Ia and the input current Id2. The generated current Ia fluctuates between Ia=0 [A] and 10 [A], and the input current Id2 is Id2=0 [A]. In contrast, B in Fig. 11 shows Vd = Ve. It can be seen that the voltage Vd is controlled to the target value by the voltage and current control system of the INV 24, although there is a steady-state deviation. C in Fig. 11 shows the inverter current Iinv. When the amount of power generated by the power generation unit 4 fluctuates, the inverter current Iinv repeats between 0 [A] and a finite value at a constant cycle.

[0126] <Effects of Example 3> According to the third embodiment, any one of the following effects can be obtained. (1) The configuration shown in the second embodiment described above can be realized, and the same effects as those of the second embodiment can be obtained. (2) By the charging and discharging operation of the power storage section 6 in the third embodiment, the weak power obtained from the power generation unit 4 can be charged into the capacitor 12, and the generated power can be recovered regardless of the magnitude of the generated power.

[0127] (3) According to the third embodiment, there is no need to use an element such as a switch to switch between charging and discharging depending on the level of generated power. Even if the level of generated power fluctuates, the generated power can be recovered seamlessly and effectively utilized. (4) The DC-DC16 required in the first and second embodiments can be omitted, and the INV24 can achieve the same power storage effect as in the first and second embodiments, while omitting the DC-DC16 can simplify the configuration. EXAMPLES

[0128] In the first embodiment shown in FIG. 3, the control units 16-4, 18-4, voltage sources 46, 78, triangular wave generator 56, comparison amplifiers 52, 54, inverters 60, 84 and buffer amplifiers 58, 62, 82, 86 may be configured with digital circuits such as microcomputers to realize the functions described above.

[0129] In the second embodiment shown in FIG. 6, the control units 16-4, 18-6, voltage sources 46, 98, triangular wave generator 56, comparison amplifiers 52, 54, inverters 60, 84 and buffer amplifiers 58, 62, 82, 86 may be configured with digital circuits such as microcomputers to realize the functions described above.

[0130] In the third embodiment shown in FIG. 9, the control units 18-4, 24-4, comparison amplifiers 52, 54, triangular wave generator 56, voltage source 132, AC source 134, inverters 84, 142 and buffer amplifiers 82, 86, 138, 140, 144, 146 may be configured with digital circuits such as microcomputers to realize the functions described above.

[0131] When configuring a control system using digital circuits in this manner, it is sufficient to have a processor, an input / output section, a memory section, etc., and have the processor execute a control program stored in the memory section, and have the memory section equipped with storage elements such as a ROM (Read-Only Memory) or a RAM (Random-Access Memory), and to realize the functions described above using control patterns and various types of control information.

[0132] <Effects of Example 4> According to the fourth embodiment, any one of the following effects can be achieved. (1) The control system can be simplified, and a variety of control modes can be realized through digital processing, resulting in highly efficient power recovery. (2) Digitalization of the control system reduces the number of parts and reduces costs.

[0133] Other Embodiments This disclosure includes the following embodiments or examples. (1) The power generation system or power storage device disclosed herein may be configured without including INV20 or INV24. The INV20 may be configured with only a DC-DC converter without an inverter function.

[0134] (2) If the power generated by the power generating unit 4 is, for example, lkW or more, the power generation voltage Va may be controlled to a constant value. If the power generated is less than lkW, Id may be controlled to be constant at the upper and lower limits of the charging voltage Vc of the capacitor 12. If the charging voltage Vc is less than the lower limit, control may be performed to stop the DC-DC 16. Also, if the sunlight received by the solar panel 10 is weak, control may be performed to lower the charging voltage Vc of the capacitor 12 in preparation for the next power generation. (3) Regarding charging and discharging of the battery 14, a mode switching may be performed such that charging occurs during the day and discharging occurs at night.

[0135] As described above, the most preferred embodiment of the present disclosure has been described. The present disclosure is not limited to the above description. Based on the gist of the present disclosure described in the claims or disclosed in the form for carrying out the present disclosure, various modifications and changes are possible for those skilled in the art. It goes without saying that such modifications and changes are included in the scope of the present disclosure. [Industrial Applicability]

[0136] According to the energy storage device, energy storage method, and power generation system disclosed herein, by adding the storage of an energy storage device, it is possible to recover the power generation output, which varies greatly from very low power to very high power output by the power generation unit, while reducing internal power consumption, thereby increasing the recovery rate or utilization rate of the generated power. [Explanation of symbols]

[0137] 2. Power generation system 4 Power Generation Unit 6. Power storage unit 8 Power Conditioner 10-1, 10-2, ..., 10-n Solar power panels 12, 88 Capacitor 13. Voltmeter 14 Battery 15 Ammeter 16, 18 DC-DC converter 16-2, 18-2 Converter section 16-4, 18-4, 18-6, 24-4 Control section 16-42, 18-62 Voltage control section 16-44, 18-64 Current control section 20, 24 INV 21, 21-1, 21-2 Output terminal 22 Output terminal 24-2 Inverter section 28, 30, 64, 66, 104, 106, 108, 110 transistors 32, 34, 68, 70, 112, 114, 116, 118 Diodes 36 Choke coil 38, 42, 74, 92, 94, 122, 128 Adder 40, 44, 76, 90, 96, 124, 130 Coefficient Amplifier 46, 78, 98, 132 Voltage Source 48, 100 Isolation amplifier 50, 80, 136 Hall elements 52, 54 Comparison amplifier 56 Triangle Wave Generator 58, 62, 82, 86, 138, 140, 144, 146 Buffer amplifiers 60, 84, 142 inverter 72, 120 Choke coil 79 Reference potential point 102 AC power supply 126 Multiplier 134 AC source

Claims

1. a power storage section that connects at least a series circuit of a capacitor and a secondary battery in parallel with a power generation unit and stores the power generated by the power generation unit; a first DC-DC converter connected to the power generation unit and the capacitor, and configured to control a storage voltage of the power storage unit to a target value by using any one of a generated current, a generated voltage, or a generated power of the power generation unit; a second DC-DC converter connected to the secondary battery and configured to control a current obtained from the secondary battery of the power storage unit, which is charged or discharged in accordance with the generated power, to a target value; wherein the capacitor is connected between an input terminal of the first DC-DC converter and an input terminal of the second DC-DC converter.

2. A storage unit that connects at least a series circuit of a capacitor and a secondary battery in parallel with a power generation unit and stores the power generated by the power generation unit; a first DC-DC converter connected to the power generation unit and the capacitor, and configured to control a storage voltage of the power storage unit to a target value by using any one of a generated current, a generated voltage, or a generated power of the power generation unit; a second DC-DC converter that is connected to the secondary battery and controls the output voltage to a target value by using a current and an output voltage flowing through the secondary battery of the power storage unit that charges or discharges the secondary battery in accordance with the generated power; wherein the capacitor is connected between an input terminal of the first DC-DC converter and an input terminal of the second DC-DC converter.

3. A storage unit that connects at least a series circuit of a capacitor and a secondary battery in parallel with a power generation unit and stores the generated power of the power generation unit; an inverter connected to the power generation unit and the power storage unit to convert the generated power into AC power and to control the storage voltage of the power storage unit to a target value by using an output current and a storage voltage of the power storage unit; A power storage device comprising:

4. The energy storage device as described in claim 3, further comprising a DC-DC converter connected to the secondary battery and installed between the secondary battery and the inverter, for controlling the current obtained in the secondary battery of the energy storage unit, which charges or discharges in accordance with the generated power, to a target value.

5. An energy storage device as described in claim 1, claim 2, claim 3 or claim 4, wherein the power generation unit is a solar power generation panel.

6. a step of storing the generated power of the power generation unit by connecting a series circuit of at least a capacitor and a secondary battery in parallel with the power generation unit; a step of a first DC-DC converter connected to the power generating unit and the capacitor controlling a storage voltage of the power storage unit to a target value using any one of a generated current, a generated voltage, or a generated power of the power generating unit; a step of controlling a current obtained by a second DC-DC converter connected to the secondary battery between an input terminal of the second DC-DC converter and an input terminal of the first DC-DC converter and the capacitor, the current being charged or discharged in accordance with the generated power, to a target value; The method of storing electricity includes:

7. a step of storing the generated power of the power generation unit by connecting a series circuit of at least a capacitor and a secondary battery in parallel with the power generation unit; a step of a first DC-DC converter connected to the power generating unit and the capacitor controlling a storage voltage of the power storage unit to a target value using any one of a generated current, a generated voltage, or a generated power of the power generating unit; a second DC-DC converter connected to the secondary battery is connected to the capacitor between an input terminal of the second DC-DC converter and an input terminal of the first DC-DC converter, and the output voltage of the secondary battery of the power storage unit is controlled to a target value by using a current and an output voltage flowing through the secondary battery of the power storage unit, which is charged or discharged according to the generated power; The method of storing electricity includes:

8. a step of storing the generated power of the power generation unit by connecting a series circuit of at least a capacitor and a secondary battery in parallel with the power generation unit; an inverter connected to the power generation unit and the power storage unit and converting power generated by the power generation unit into AC power; a step of controlling, by the inverter, a storage voltage of the power storage unit to a target value by using an output current of the inverter and a storage voltage of the power storage unit; The method of storing electricity includes:

9. The energy storage method described in claim 6, claim 7 or claim 8, wherein the power generation unit is a solar power generation panel.

10. A power generation unit that generates DC power; The power storage device according to claim 1, claim 2, claim 3, claim 4 or claim 5; A power generation system comprising:

11. The power generation system according to claim 10 , wherein the power generation unit is a solar power generation panel.

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