JP3792711B1 - Charger - Google Patents

Abstract

In a charging device that charges an electric double layer capacitor (hereinafter referred to as a “capacitor”) with a solar cell, the output of the solar cell to the capacitor is controlled in order to improve the charging efficiency of the capacitor by the solar cell.
A charging device includes at least a switch, and a step-down switching regulator that converts power supplied from a solar cell to a capacitor in accordance with a variable duty ratio of the switch; The circuit 57 for detecting the output current of the battery, the duty ratio control unit 84 for controlling the duty ratio of the switch, the circuit 50 for detecting the current of the capacitor, and the output current of the solar battery without referring to the voltage of the capacitor A command value supply unit 60 that discretely changes the command value and supplies the command value to the duty ratio control unit is included. The command value supply unit discretely changes the command value so that the capacitor current is substantially maximized based on the characteristics of the temporal change of the capacitor current associated with each discrete change.
[Selection] Figure 1

Description

  The present invention relates to a technology for charging an electric double layer capacitor with a solar cell, and more particularly to a technology for controlling the output of the solar cell to the electric double layer capacitor in order to improve the charging efficiency of the electric double layer capacitor by the solar cell. .

  There is a solar cell as an example of a power generation element that uses natural energy to generate electrical energy. There is also an electric double layer capacitor (hereinafter simply referred to as “capacitor”) as an example of a storage element that stores electric energy generated by such a power generation element.

  Generally, a solar cell has a characteristic that generated power has a maximum point with respect to a generated voltage and a generated current. Therefore, when using a solar cell, when the power generation voltage or power generation current of the solar cell changes, the generated power, that is, the output of the solar cell changes accordingly.

  Therefore, in order to charge a capacitor with a solar cell, in one example of a charging device that is used connected to the solar cell and the capacitor, switching control for converting the DC voltage generated by the solar cell and supplying the converted voltage to the capacitor A circuit is used. This switching control circuit has a function of controlling the output of the solar cell to the electric double layer capacitor in order to increase the charging efficiency of the capacitor by the solar cell.

  There is a conventional example of a charging device that is used by being connected to a solar cell and a capacitor having the characteristics and characteristics described above (see, for example, Patent Document 1). This conventional example includes a switching converter having a switch, a coil, and a diode, a current detection circuit that detects a power generation current of the solar battery, a voltage detection circuit that detects a power generation voltage of the solar battery, the switching converter and the current detection. A controller is connected to the circuit and the voltage detection circuit.

In this conventional example, the controller sets the duty ratio of the switch so that the generated power of the solar cell is maximized based on the generated current detected by the current detecting circuit and the generated voltage detected by the voltage detecting circuit. Determine the optimal value. This controller controls the on / off state of the switch so that the optimum value of the determined duty ratio is realized.
JP 2002-199614 A

  By the way, the capacitor has a feature that the voltage largely changes in accordance with the amount of charge accumulated in the capacitor, that is, the amount of stored energy. This feature is unique to the capacitor and does not exist in other types of power storage elements such as secondary batteries including lead storage batteries.

  Capacitors are categorized as physical cells that extract electrical energy from physical changes, similar to solar cells, while secondary cells, like primary cells and fuel cells, extract electrical energy from chemical reactions. It is classified as a chemical battery to be taken out.

  However, in the above-described conventional example, the output of the solar cell is unilaterally determined from the power generation state of the solar cell without referring to the charged state of the capacitor. Therefore, in this conventional example, there is a limit in improving the charging efficiency of the electric double layer capacitor by the solar cell.

  Against the background described above, the present invention relates to a technology for charging an electric double layer capacitor with a solar cell, in order to improve the charging efficiency of the electric double layer capacitor with the solar cell, The task is to determine the output more accurately.

  The following aspects are obtained by the present invention. Each aspect is divided into sections, each section is given a number, and is described in a form that cites other section numbers as necessary. This is to facilitate understanding of some of the technical features that the present invention can employ and combinations thereof, and the technical features that can be employed by the present invention and combinations thereof are limited to the following embodiments. Should not be interpreted. That is, it should be construed that it is not impeded to appropriately extract and employ the technical features described in the present specification as technical features of the present invention although they are not described in the following embodiments.

  Further, describing each section in the form of quoting the numbers of the other sections does not necessarily prevent the technical features described in each section from being separated from the technical features described in the other sections. It should not be construed as meaning, but it should be construed that the technical features described in each section can be appropriately made independent depending on the nature.

(1) Electric power generated by a solar cell having a maximum point with respect to a generated voltage and a generated current is stored in the electric energy generated by the solar cell, and the voltage changes depending on the amount of the stored energy. A charging device used to connect the solar cell and the electric double layer capacitor to charge the multilayer capacitor,
A step-down switching regulator that has at least a switch and converts electric power supplied from the solar cell to the electric double layer capacitor according to a variable duty ratio of the switch;
An output current detection circuit that detects, as an actual output current, an actual value of a current output from the solar cell to the electric double layer capacitor via the switching regulator;
A duty ratio control unit that is connected to the switching regulator and the output current detection circuit, and controls the duty ratio so that the detected value of the actual output current by the output current detection circuit matches the command value of the target output current;
A capacitor current detection circuit for detecting a current of the electric double layer capacitor as a capacitor current;
The duty ratio control unit and the capacitor current detection circuit are connected to each other, and the command value of the target output current is discretely changed and supplied to the duty ratio control unit without referring to the voltage of the electric double layer capacitor. Including the command value supply section,
The command value supply unit discretely changes the command value of the target output current so that the capacitor current is substantially maximized based on the characteristics of the time change of the capacitor current with each discrete change. Charging device.

  In general, in this type of charging device, it is ultimate that the electric power taken from the solar cell to the electric double layer capacitor (hereinafter simply referred to as “capacitor”) is maximized, that is, the charging power of the capacitor is maximized. Purpose.

  On the other hand, in the above-described conventional example, if the switch for controlling the flow of electric energy from the solar cell to the capacitor is controlled so that the generated power of the solar cell is maximized, the charging power of the capacitor is also maximized. Based on the assumption of linear dependence, the switch is controlled so that the power generated by the solar cell is maximized.

  However, the dependency relationship is not necessarily established in all charging devices. For example, in an environment in which an electric circuit that supplies electric energy from a solar cell to a capacitor is configured as a linear circuit in the charging device, the linear dependency relationship is established.

  On the other hand, in an environment where the electric circuit includes a non-linear element (for example, many semiconductor elements including a diode), the linear dependence relationship is not established. For this reason, when the above-described conventional example is implemented, the generated power of the solar cell is maximized, but the charging power of the capacitor is not maximized.

  In the charging device according to this section, the command value of the target output current of the solar cell is determined so that the charging current of the capacitor is substantially maximized and the charging power of the capacitor is substantially maximized.

  Therefore, according to this charging device, regardless of the characteristics of the electric circuit between the solar cell and the capacitor, it is easy to reliably achieve the ultimate purpose of maximizing the power taken into the capacitor from the solar cell. It becomes.

  In general, a person skilled in the art can come up with detecting a charging current and a charging voltage of a capacitor by a detection circuit in order to monitor the charging power of the capacitor. This is because the power flowing from the solar cell to the capacitor through the switch is represented by the product of the charging voltage and the charging current, and, as described above, unlike the chemical battery, the voltage changes as the charging proceeds in the capacitor. It is because it has the property to do.

  However, as a result of research, the present inventor has found that the charging voltage of the capacitor is almost constant even if charging of the capacitor proceeds if observed within a short time range. This will be specifically described below.

  In a chemical battery, in almost the entire charging period, the charging voltage is constant if the charging current is constant, whereas the charging voltage changes when the charging current changes. However, when the chemical battery approaches a fully charged state, the charging voltage increases even if the charging current is constant.

  This is because, prior to the transition to the fully charged state, a voltage corresponding to the chemical reaction inherent to the chemical battery, that is, the energy gap of the substance constituting the chemical battery, is generated. This is because a chemical reaction (for example, electrolysis of water) occurs in place of the original chemical reaction.

  Therefore, in the chemical battery, as long as it is before the transition to the fully charged state, there is a period in which the charging voltage is substantially constant. However, in a chemical battery, a period in which the charging voltage is substantially constant exists on the condition that the charging current is constant.

  On the other hand, according to the knowledge of the present inventors, in a capacitor, regardless of whether the charging current is constant or not throughout the charging, the charging voltage is constant if observed within a short time range. Can be considered.

  In order to store electric energy, a capacitor uses a physical phenomenon of charge accumulation in an electric double layer in the capacitor. Therefore, although the charging voltage rises as the charging progresses, if it is within a short time range, the characteristic that the change in the charging voltage is so small that it can be ignored with respect to the control error of the charging power is significantly different from the chemical battery Has different properties. In addition, unlike a chemical battery, a capacitor does not cause a phenomenon that a charging voltage increases in a fully charged state.

  Therefore, in the short time range, the present inventor sufficiently determines whether the charging power of the capacitor is large or small even if the charging voltage of the capacitor is not considered even if the charging current of the capacitor is considered. I realized I could do it accurately.

  Based on the knowledge explained above, in the charging device according to this section, the charging current of the capacitor is referred to, but the charging voltage of the capacitor is not referred to, and the charging current of the capacitor is substantially maximized. A command value for the target output current of the solar cell is determined.

  As a result, in this charging apparatus, as a result, the command value of the target output current of the solar cell is determined so that the charging power of the capacitor is substantially maximized, and the solar cell target value is determined to the determined command value. The duty ratio of the switch is determined so that the actual output currents match.

  Therefore, according to this charging device, it is easier to simplify the electric circuit for the detection than to detect not only the charging current of the capacitor but also the charging voltage in order to monitor the charging power of the capacitor. It becomes.

  Japanese Patent No. 3267054 discloses a power storage device that charges a storage battery with a solar battery. Specifically, the power storage device includes a transformer means for changing the power generation voltage of the solar cell, a detector means for detecting a charging current of the storage battery by the solar battery, and a transformer means for maximizing the detected charging current. And a control means for controlling.

  In the publication, “in general, the charging voltage Vb of the storage battery 12 is substantially constant during the charging operation, and therefore the point at which the generated power P of the solar battery 10 is maximized is that the charging current Ib (of the storage battery 12) is the maximum. Is almost equal to the point.

  Judging from this description, the “storage battery 12” in the publication is a battery classified as a secondary battery (chemical battery) represented by a lead storage battery, and is different from the “capacitor” in the charging device according to this section. .

  Certainly, the capacitor, which is a chemical battery and a physical battery, is common to each other in that it has a function of storing electric energy, and is also common to each other in that there is a period in which the charging voltage is substantially constant.

  Therefore, it may seem easy for those skilled in the art to implement the technique disclosed in the publication in the technique of charging a capacitor with a solar cell.

  However, those skilled in the art have recognized that a capacitor is a battery whose charging voltage increases as charging progresses, and those skilled in the art are familiar with chemical batteries, and the technology for charging chemical batteries is used in capacitors. It is natural to think that can not be implemented.

  Nevertheless, the present inventor has obtained the knowledge that “a capacitor has a substantially constant charging voltage as long as it is within a short time range”, and only applies the capacitor to the charging device. The present inventors have come up with a technique for controlling the output of a solar cell without referring to the charging voltage, but referring to the charging voltage.

  As described above, there is a period in which the charging voltage changes even in the case of a chemical battery. Therefore, in order to control the output of the solar cell with high accuracy by focusing on the charging current only during the period when the charging voltage is constant. It is necessary to confirm that the charging current is constant.

  On the other hand, with regard to capacitors, as long as the length of the control cycle of interest is managed, regardless of whether or not the charging current is constant, the output of the solar cell can be controlled with high precision, focusing on the charging current. Can do.

  Moreover, the chemical battery has an internal resistance. Therefore, when a chemical battery is charged with a load that consumes power (particularly, a load whose power consumption fluctuates with time) being connected in parallel, the charging current of the chemical battery changes greatly. As a result, the charging voltage of the chemical battery also changes.

  On the other hand, in this capacitor, there is no phenomenon corresponding to the internal resistance in a chemical battery, so even when the capacitor is charged with a load connected in parallel, it is observed within a short time range. Then, it can be considered that the charging voltage is constant.

  Thus, when comparing the environment for charging the chemical battery and the environment for charging the capacitor with respect to the stability of the charging voltage, the latter environment is more stable as the control accuracy of the output of the power generation battery is higher. In addition, the latter environment is more stable as the fluctuation of the charging current of the storage battery is larger.

  As is clear from the above description, according to the charging device according to this section, the capacitor that has been recognized as being unstable in voltage than the chemical battery is controlled from the viewpoint of a short control cycle, thereby There is no such viewpoint so far, since the battery is switched to a battery that is stable in terms of voltage.

  An example of a “switching regulator” in this section is configured to include a switch, a coil, and a diode, and another example is a synchronization that includes a switch, a coil, and a transistor or FET of a commutation circuit. It is configured as a rectification method.

(2) The command value supply unit repeats a subcycle in which the command value is discretely changed by a step size for each search cycle so that the capacitor current is substantially maximized. Exploring the optimum value of the target output current,
The cycle of the sub-cycle includes E (Wh) as the stored energy of the electric double layer capacitor, P (W) as the generated power of the solar cell, and the charging voltage Vc of the electric double layer capacitor as a control error of the charging voltage Vc. When the control error rate obtained by dividing by ΔVc is expressed by γ,
(E / P) · γ
The charging device according to item (1), wherein the charging device is set so as not to exceed a value represented by using.

  In the charging device according to the item (1), the output current of the solar cell is discretely changed. Therefore, there is a control error in the capacitor charging current that responds to the step size of the output current of the solar cell.

  On the other hand, as described above, the charging device according to the item (1) states that “the charging voltage of the capacitor does not change within a short time, and therefore the charging power of the capacitor is proportional to the charging current of the capacitor”. The inventor's knowledge, that is, the principle proposed by the inventor is used.

  Strictly speaking, however, the capacitor voltage changes due to the charging of the capacitor, even within a short time. “Capacitor charging voltage is constant” means that the amount of change in voltage of the capacitor is smaller than the amount of change in charge voltage of the capacitor in response to discrete changes in the output current of the solar cell.

  Based on the above knowledge, in the charging device according to this section, the subcycle in which the command value is discretely changed by the increment is repeated for each search cycle, whereby the capacitor current is substantially maximized. Thus, the optimum value of the target output current of the solar cell is determined exploratively.

Further, in this charging device, the cycle of the sub-cycle is that the stored energy of the electric double layer capacitor is E (Wh), the generated power of the solar cell is P (W), and the charging voltage Vc of the electric double layer capacitor is the charging voltage. When the control error rate obtained by dividing by the control error ΔVc of Vc is expressed by γ,
(E / P) · γ
It is set so as not to exceed the value represented by.

  In an example in which the generated power of the solar cell, that is, the output P is 10 (W) and the stored energy of the capacitor, that is, the storage capacity E is 10 (Wh), if the electrical loss of the charging device is ignored, the specific output 1 (h) is required to fully charge a capacitor having the specific storage capacity with a solar cell having a 1/100 (h) ), That is, 36 (s) is required.

Stored energy Q of the capacitor, since equal to half (= CVc ^2/2) of the product of the square and the capacitance C of the voltage Vc of the capacitor, in the vicinity of full charge of the capacitor, the voltage Vc of the capacitor When it changes by 1%, the stored energy Q changes by about 2% (= 1.01 ² -1.00 ² ). In the vicinity of charging (50% charging) where the charging voltage is ½ of the total charging voltage, if the voltage Vc of the capacitor changes by 1%, the stored energy Q is about 1% (= 0.51 ² −0). .50 ² ) Change.

  Therefore, in this example, the time for the charge voltage to change by 1% is 72 (s) near full charge and 36 (s) near 50% charge.

  Therefore, in the charging device according to this section, assuming that the control error rate γ is 0.01, the period of the sub cycle, that is, the length of time for which the latest value of the command value is held is 72 (s). And 36 (s) are set so as not to exceed the shorter one.

  In this example, the period of the subcycle is set to 36 (s). However, this example is merely an example for explanation, and the period of the subcycle is actually in the order of 10 ms, for example, 100 ms. It is set in order or 1s order.

(3) The duty ratio control unit is configured using an analog circuit that repeats the switching operation of the switch in a switching cycle,
The command value supply unit executes a plurality of subcycles for each search cycle, and is configured using a computer to discretely change the command value by a step size for each subcycle,
The charging apparatus according to (1) or (2), wherein the duty ratio control unit causes the switch to perform a plurality of switching operations that share the duty ratio for each subcycle.

  In this charging apparatus, the duty ratio control unit repeatedly performs the switching operation of the switch in the switching cycle. Further, the command value supply unit executes a plurality of subcycles for each search cycle, and discretely changes the command value by a step size for each subcycle.

  Furthermore, in this charging apparatus, the duty ratio control unit causes the switch to perform a plurality of switching operations with a common duty ratio for each subcycle.

  Therefore, in this charging apparatus, the operation cycle of the duty ratio control unit is shorter than the operation cycle of the command value determination unit, and therefore the duty ratio control unit operates faster than the command value determination unit. Is required. Therefore, when both the duty ratio control unit and the command value supply unit are configured using a computer, the duty ratio control unit is configured using an analog circuit, whereas the command value supply unit is configured using a computer. The computational load of the computer increases.

  Therefore, in the charging device according to this section, the duty ratio control unit prioritizes high-speed processing and is configured using an analog circuit, while the command value supply unit prioritizes operation freedom and uses a computer. It is configured.

(4) The charging device according to any one of (1) to (3), wherein the charging device is operated in a state where a load that consumes power is connected in parallel to the electric double layer capacitor.

  As described above, unlike a chemical battery, a capacitor does not have an internal resistance. Therefore, even if the capacitor is charged in a state where a load that consumes power is connected in parallel, the charging voltage of the capacitor does not decrease due to power consumption by the load. Further, even if the power consumption of the load fluctuates with time, fluctuation of the charging voltage due to the fluctuation is avoided.

  Based on such knowledge, in the charging device according to this section, the capacitor is charged by the solar cell in a state where a load that consumes power is connected in parallel to the capacitor.

  However, it is not indispensable for this charging device to be used in such a manner that the load is always connected in parallel to the capacitor, and only when the capacitor is not being charged, the load is connected in parallel to the capacitor (that is, charging) Some of them can be used in a manner in which a load is not connected in parallel to the capacitor.

(5) The command value supply unit repeats a subcycle in which the command value is discretely changed by a step size for each search cycle so that the capacitor current is substantially maximized. Exploring the optimum value of the target output current,
The command value supply unit
In each sub-cycle, based on the characteristic of the command value change in the previous sub-cycle and the characteristic of temporal change in the capacitor current in the previous sub-cycle, the time of the capacitor current in the current sub-cycle In order to reduce the amount of change, the change direction in which the command value is changed from the previous subcycle in the current subcycle, and the step size used to determine the command value in the current subcycle, A first determination unit for determining
In each of the subcycles, the command value used in the previous subcycle is discretely changed based on the determined change direction and the size of the step size, thereby being used in the current subcycle. The charging device according to any one of (1) to (4), including: a second determination unit that determines the command value.

  In this charging device, the command value is changed from the previous subcycle in the current subcycle based on the characteristics of the command value change in the previous subcycle and the characteristics of the temporal change in the capacitor current in the previous subcycle. The change direction to be determined and the size of the step size used for determining the command value in the current sub-cycle are determined.

  Further, based on the determined change direction and step size, the command value used in the previous sub cycle is discretely changed, thereby determining the command value used in the current sub cycle. The

(6) The change characteristic of the command value includes a direction of change of the command value,
The characteristic of the time change of the capacitor current includes the direction of time change of the capacitor current.

(7) In the first sub-cycle, the first determination unit determines the size of the step size so that the smaller the amount of temporal change in the capacitor current in the previous sub-cycle, the smaller the step size. The charging device according to (5) or (6), including a step size determination unit.

  As will be described in detail later, the capacitor current changes so as to have a maximum value with respect to a unidirectional change in the output current of the solar cell (as shown in a convex graph as shown in FIG. 8). . The output current of the solar cell corresponding to the maximum value is the optimum value of the output current.

  Therefore, as the capacitor current approaches its local maximum, the changing slope of the capacitor current with respect to the output current of the solar cell decreases. This means that the amount of temporal change in capacitor current between adjacent subcycles is reduced.

  On the other hand, reducing the step size of the output current of the solar cell as the capacitor current approaches its maximum value is effective for searching for the maximum value of the capacitor current with higher accuracy.

  In addition, in a region where the capacitor current is far from its maximum value, increasing the step size of the output current of the solar cell in a region close to the maximum value will result in a search for the maximum value of the capacitor current in a shorter time. It is effective to do.

  Based on such knowledge, in the charging device according to this section, in each sub-cycle, 1% of the output current of the solar cell is reduced so that the amount of temporal change of the capacitor current in the previous sub-cycle decreases. A discrete change amount per round, that is, the size of the step size is determined.

(8) The first determining unit may reduce the step size so that the smaller the current difference, which is the difference between the output current of the solar cell and the capacitor current in the previous subcycle, is smaller in each subcycle. The charging device according to any one of (5) to (7), including a second step size determination unit that determines a size.

  Generally, in a switching regulator, when the switch duty ratio is 100%, that is, when the switch is kept on in one switching cycle, the power conversion action of the switching regulator (for example, change in current flowing in the circuit under self-inductance) (A phenomenon in which electromotive force is induced in the circuit due to this) is not performed.

  When the power conversion action of the switching regulator is not performed, the current and voltage between the solar cell and the capacitor become equal to each other, and as a result, the output current of the solar cell reaches an optimum value for substantially maximizing the capacitor current. Neither can the output voltage be controlled.

  On the other hand, the power conversion action of the switching regulator is smaller as the current difference, which is the difference between the output current of the solar cell and the capacitor current, is smaller.

  Based on the knowledge explained above, in the charging device according to this section, in each sub-cycle, the smaller the current difference that is the difference between the output current of the solar cell and the capacitor current in the previous sub-cycle, the smaller the step. The size of the width is determined.

  Therefore, according to this charging device, the power conversion action of the switching regulator is not performed due to the switch being kept on, and as a result, the output current of the solar cell and the capacitor current are not optimized. Can be avoided.

  In this charging device, the output current of the solar cell and the capacitor current are detected respectively, and the current difference may be directly monitored as the difference between the detected values, but the physical quantity reflecting the current difference is detected, You may monitor a current difference indirectly using the detected value.

  For example, when the charging device uses a differential amplifier that operates proportionally according to the difference between the command value of the target output current and the actual output current of the solar battery, the output of the differential amplifier is output when the switch is kept on. The voltage will exceed the set voltage. Therefore, the difference between the output voltage of the differential amplifier and the set voltage may be detected, and the current difference may be indirectly monitored using the detected value.

(9) The switch performs a switching operation in accordance with the input on / off command signal,
The output current detection circuit outputs an analog signal representing the magnitude of the actual output current,
The capacitor current detection circuit outputs an analog signal representing the magnitude of the capacitor current,
The command value supply unit
An AD converter that converts an analog signal input from the capacitor current detection circuit into a digital signal;
A computer for determining the command value as a digital signal based on the digital signal output from the AD converter;
A digital-to-analog converter that converts a digital signal output from the computer into an analog signal;
The duty ratio controller is
A differential amplifier for performing differential amplification based on two analog signals respectively input from the output current detection circuit and the DA converter;
A triangular wave source for generating an analog signal representing a triangular wave, and the levels of two analog signals respectively input from the triangular wave source and the differential amplifier are compared with each other, and an on / off command signal representing the comparison result is output to the switch. The charging device according to any one of (1) to (8), including a comparator.

(10) Electric power generated by a solar cell having a maximum point with respect to the generated voltage and generated current is stored in the electric energy generated by the solar cell, and the voltage changes depending on the amount of the stored energy. A charging device used to connect the solar cell and the electric double layer capacitor to charge the multilayer capacitor,
A step-down switching regulator that has at least a switch and converts electric power supplied from the solar cell to the electric double layer capacitor according to a variable duty ratio of the switch;
An output voltage detection circuit for detecting an actual value of a voltage output from the solar cell to the electric double layer capacitor through the switching regulator as an actual output voltage;
A duty ratio control unit that is connected to the switching regulator and the output voltage detection circuit, and controls the duty ratio so that the detected value of the actual output voltage by the output voltage detection circuit matches the command value of the target output voltage;
A capacitor current detection circuit for detecting a current of the electric double layer capacitor as a capacitor current;
The duty ratio control unit and the capacitor current detection circuit are connected to each other and the command value of the target output voltage is discretely changed and supplied to the duty ratio control unit without referring to the voltage of the electric double layer capacitor. Including the command value supply section,
The command value supply unit discretely changes the command value of the target output voltage so that the capacitor current is substantially maximized based on the characteristics of the time change of the capacitor current accompanying the discrete change of each time. Charging device.

  According to this charging apparatus, basically the same operation and effect are realized according to the principle that is basically common to the charging apparatus according to the item (1).

  This charging device adopts the technical features described in any one of the items (3), (4), and (6) to (9) with modifications necessary for applying to the charging device. Is possible.

(11) The command value supply unit repeats a subcycle for discretely changing the command value by a step size for each search cycle so that the capacitor current is substantially maximized. Exploratively determine the optimal value of the target output voltage,
The cycle of the sub-cycle includes E (Wh) as the stored energy of the electric double layer capacitor, P (W) as the generated power of the solar cell, and the charging voltage Vc of the electric double layer capacitor as a control error of the charging voltage Vc. When the control error rate obtained by dividing by ΔVc is expressed by γ,
(E / P) · γ
The charging device according to (10), wherein the charging device is set so as not to exceed a value represented by using.

  According to this charging apparatus, basically the same operation effect is realized according to the principle that is basically common to the charging apparatus according to the item (2).

(12) The command value supply unit repeats a subcycle for discretely changing the command value by a step size for each search cycle so that the capacitor current is substantially maximized. Exploratively determine the optimal value of the target output voltage,
The command value supply unit
In each sub-cycle, based on the characteristic of the command value change in the previous sub-cycle and the characteristic of temporal change in the capacitor current in the previous sub-cycle, the time of the capacitor current in the current sub-cycle In order to reduce the amount of change, the change direction in which the command value is changed from the previous subcycle in the current subcycle, and the step size used to determine the command value in the current subcycle, A first determination unit for determining
In each of the subcycles, the command value used in the previous subcycle is discretely changed based on the determined change direction and the size of the step size, thereby being used in the current subcycle. The charging device according to (10) or (11), including: a second determination unit that determines the command value.

  According to this charging apparatus, basically the same function and effect are realized according to the principle that is basically common to the charging apparatus according to the item (5).

(13) Electric power generated by a solar cell having a local maximum point with respect to the generated voltage and generated current is stored in the electric energy generated by the solar cell and the voltage varies depending on the amount of the stored energy. A charging device used to connect the solar cell and the electric double layer capacitor to charge the multilayer capacitor,
A step-down switching regulator that has at least a switch and converts electric power supplied from the solar cell to the electric double layer capacitor according to a variable duty ratio of the switch;
An output current detection circuit that detects, as an actual output current, an actual value of a current output from the solar cell to the electric double layer capacitor via the switching regulator;
An output voltage detection circuit for detecting an actual value of a voltage output from the solar cell to the electric double layer capacitor through the switching regulator as an actual output voltage;
A current that is connected to the switching regulator, the output current detection circuit, and the output voltage detection circuit, and controls the duty ratio so that the detected value of the actual output current by the output current detection circuit matches the command value of the target output current. Duty ratio control unit that selectively performs change-type control and voltage change-type control that controls the duty ratio so that the detected value of the actual output voltage by the output voltage detection circuit matches the command value of the target output voltage When,
A capacitor current detection circuit for detecting a current of the electric double layer capacitor as a capacitor current;
The duty ratio control unit and the capacitor current detection circuit are connected to each other, and (a) iteratively changes the command value of the target output current, and changes the capacitor current with time according to each discrete change. A current change type control that determines a command value of the target output current so that the capacitor current is substantially maximized, and supplies the determined command value to the duty ratio control unit; b) Iteratively changing the command value of the target output voltage repeatedly, so that the capacitor current is substantially maximized based on the characteristics of the change in the capacitor current with each discrete change. A command value supply unit that determines a command value of the target output voltage and selectively performs voltage change type control that supplies the determined command value to the duty ratio control unit,
The command value supply unit performs the current change type control when the actual output voltage is higher than a reference value, while the voltage change type control when the actual output voltage is not higher than the reference value. To perform the charging device.

  Paying attention to the characteristics of the solar cell shown in FIG. 8, the target output current is changed because the slope of the voltage with respect to the current is gentler in the high region of the entire range of the actual output voltage of the solar cell than in the low region. It is possible to detect the optimum value of the target output current with higher accuracy than to change the target output voltage.

  On the other hand, in the low region of the entire range of the actual output voltage of the solar cell, the gradient of the current with respect to the voltage is gentler than in the high region, so changing the target output voltage changes the target output current. As a result, the optimum value of the target output current can be detected with high accuracy.

  Based on the knowledge described above, in the charging device according to this section, when the actual output voltage of the solar cell is higher than the reference value, the current change type that repeats discretely changing the command value of the target output current On the other hand, when the actual output voltage is not higher than the reference value, the voltage change type control that repeats changing the command value of the target output voltage discretely is performed.

  This charging apparatus adopts the technical features described in any one of the items (2) to (9), (11), and (12), with modifications necessary for applying to the charging apparatus. Is possible.

  Hereinafter, some of more specific embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an electric circuit diagram of a charging device 10 according to a first embodiment of the present invention together with a solar cell 12 and an electric double layer capacitor (hereinafter simply referred to as “capacitor”) 14. FIG. 1 also shows a load 16 (for example, an electric device such as a lighting fixture or a motor) that consumes the electric energy generated by the solar cell 12.

  As shown in FIG. 1, the charging device 10 has a positive electrode line 20 and a negative electrode line 22. The positive electrode line 20 has external terminals 24 and 26 at both ends, and the negative electrode line 22 has external terminals 28 and 30 at both ends. The charging device 10 is electrically connected to the positive terminal and the negative terminal of the solar cell 12 at the external terminal 24 of the positive line 20 and the external terminal 28 of the negative line 22, respectively. Further, the charging device 10 is electrically connected to the positive terminal and the negative terminal of the capacitor 14 at the external terminal 26 of the positive line 20 and the external terminal 30 of the negative line 22, respectively.

  In FIG. 1, the generated voltage of the solar cell 12 is expressed as “Vs” and the generated current is expressed as “Is”, while the charging voltage of the capacitor 14 is expressed as “Vc” and the charging current is expressed as “Ic”. Yes.

  The solar cell 12 converts solar energy into electric energy. The solar cell 12 has a characteristic that the generated power changes according to the illuminance of sunlight. The solar cell 12 also has a characteristic that the generated power has a maximum point with respect to the generated voltage Vs and the generated current Is, as shown in the graph of FIG. Therefore, when this solar cell 12 is used, when the generated voltage Vs or the generated current Is of the solar cell 12 changes, the generated power, that is, the output energy of the solar cell changes accordingly.

  FIG. 2 is a graph showing characteristics in which the generated voltage Vs and the generated current Is change under the condition that the illuminance of sunlight (= daily illuminance) is constant. In FIG. 2, the intersection between the graph and the straight line A is the optimum resistance value of the load when the charging device 10 is considered to be a load for the solar cell 12 (a resistor having a resistance value (= Vs / Is)). Therefore, it is indicated that the product of the generated current Is and the generated voltage Vs, that is, the generated power is a maximum value.

  Further, in FIG. 2, the intersection of the graph and the straight line B indicates that the generated power is not the maximum value because the resistance value of the charging device 10 as a load for the solar cell 12 is too large. In FIG. 2, the intersection between the graph and the straight line C indicates that the generated power is not the maximum value because the resistance value of the charging device 10 as a load for the solar cell 12 is too small.

  The capacitor 14 stores the electrical energy generated by the solar cell 12. The capacitor 14 is characterized in that the voltage varies greatly depending on the state of charge thereof, that is, the amount of charge accumulated in the capacitor 14. This feature is unique to the capacitor 14 and does not exist in other types of power storage elements.

  The capacitor 14 is constituted by a series connection of a plurality of individual capacitors in order to increase the energy that can be stored. In the case where it is necessary to further increase the energy that can be stored, the capacitor 14 can be configured by connecting a plurality of parallel circuits of a plurality of individual capacitors in series with each other.

  As shown in FIG. 1, the charging device 10 includes a step-down switching regulator 32.

  The switching regulator 32 includes a chopper type switch (for example, a semiconductor switch) 40, a coil (inductor) 42, and a diode (flyhole diode) 44. The switch 40 and the coil 42 are connected in series with each other in the positive electrode line 20 in that order. The diode 44 is connected to an intermediate line 46 extending from a portion of the positive electrode line 20 between the switch 40 and the coil 42 and reaching the negative electrode line 22.

  The switching regulator 32 is configured so that a voltage lower than the power generation voltage Vs of the solar cell 12 is applied to the capacitor 14, while a current larger than the power generation current Is of the solar cell 12 is supplied to the capacitor 14. 14 has a function of converting power supplied to the power supply 14.

  As is well known, the switching regulator 32 is a method of smoothing a square wave (intermittent waveform) generated by turning on and off the switch 40. This method is employed when the output voltage, that is, the charging voltage Vc of the capacitor 14 is lower than the input voltage, that is, the generated voltage Vs of the solar battery 12.

  In the switching regulator 32, the electrical energy of the solar cell 12 is stored as magnetic energy in the coil 42 via the switch 40 during a period in which the switch 40 is in an on (conducting) state. Thereafter, when the switch 40 is switched to an off (cut-off) state, the magnetic energy stored in the coil 42 is converted into electric energy by the closed circuit including the coil 42, the capacitor 14, and the diode 44 and supplied to the capacitor 14. .

  By repeatedly turning the switch 40 on and off, the electric energy of the solar cell 12 is supplied to the capacitor 14, whereby the capacitor 14 is charged by the solar cell 12.

  At this time, the charging voltage Vc of the capacitor 14 is based on the duty ratio of the switch 40, that is, the value obtained by dividing the on-time Ton when the switch 40 is on by the sum of the on-time Ton and the off-time Toff. The power generation voltage Vs of the battery 12 has a reduced height. If the voltage obtained by stepping down the generated voltage Vs becomes the charging voltage Vc, the current obtained by increasing the generated current Is of the solar battery 12 becomes the charging current Ic of the capacitor 14 in return.

  That is, the switching regulator 32 performs voltage / current conversion (power conversion) between the solar cell 12 and the capacitor 14. Specifically, the power is stored between the solar cell 12 and the capacitor 14. Under the condition, the high voltage and small current electricity in the solar cell 12 is converted into the low voltage and large current electricity in the capacitor 14. Thereby, the charging efficiency of the capacitor 14 by the solar cell 12 is improved.

  As shown in FIG. 1, the charging device 10 further includes a capacitor 48 on the upstream side of the switching regulator 32. The capacitor 48 is connected in parallel to the solar cell 12 in a state of being connected to the positive electrode line 20 and the negative electrode line 22.

  The capacitor 48 allows the electric energy to be discharged from the solar cell 12 and temporarily stores the discharged electric energy when the switch 40 is in the OFF state. On the other hand, the capacitor 48 sends the electrical energy accumulated in the capacitor 48 to the capacitor 14 via the switch 40 together with the electrical energy generated by the solar cell 12 when the switch 40 is in the ON state.

  If the charging device 10 does not include the capacitor 48, the release of electric energy from the solar cell 12 is prevented when the switch 40 is in the OFF state. Therefore, the power generation voltage Vs of the solar cell 12 is a voltage represented by a portion corresponding to the no-load state in the characteristic curve of the solar cell 12 shown in FIG. In the ON state, the voltage is represented by a portion corresponding to the amount of current flowing through the switch 40 in the characteristic curve of the solar cell 12.

  Therefore, regardless of whether the switch 40 is in an off state or an on state, the solar cell 12 is not in an optimal load state in which electric energy extracted from the solar cell 12 is maximized.

  On the other hand, in the present embodiment, as shown in FIG. 1, since the charging device 10 includes the capacitor 48, the electrical energy is released from the solar cell 12 to the capacitor 48 in the off state of the switch 40. Allowed.

  Therefore, according to the present embodiment, as a result of permitting the release of electric energy from the solar cell 12 despite the on / off control of the switch 40, the generated voltage Vs of the solar cell 12, that is, the terminal voltage of the capacitor 48 is stabilized. . Therefore, it becomes possible to maintain the solar cell 12 in the optimum load state in which the electric energy extracted from the solar cell 12 is maximized.

  In short, the capacitor 48 has a function of stabilizing the power generation voltage Vs of the solar cell 12 regardless of the on / off operation of the switch 40. In order to perform this function, it is necessary that the voltage of the capacitor 48 does not change sensitively during the switching period of the switch 40 (for example, 10 μs).

  Therefore, the capacitor 48 has a smaller capacitance than the capacitor 14. The capacitance of the capacitor 48 is set according to the length of the switching cycle of the switch 40 (for example, 10 μs), the amount of current flowing out from the solar cell 12 through the switch 40 in the ON state of the switch 40, and the like.

  As shown in FIG. 1, the charging device 10 further includes a charging current detection circuit 50 that detects the charging current Ic of the capacitor 14.

  The charging current detection circuit 50 is connected to the portion of the negative electrode line 22 between the connection point of the negative electrode terminal of the capacitor 14 and the ground point in order to detect the amount of current flowing through the capacitor 14, that is, the amount of the charging current Ic. A current detection resistor 52 is provided. The current detection resistor 52 has a function of converting a current flowing through the capacitor 14 into a voltage.

  The charging current detection circuit 50 further includes an amplifier (DC amplifier) 54 that amplifies the voltage of the current detection resistor 52 at a constant magnification. The amplifier 54 outputs an analog signal representing the charging current Ic of the capacitor 14. The amplifier 54 is configured as a DC linear amplifier, for example.

  The charging current detection circuit 50 removes a ripple component generated in the charging current of the capacitor 14 due to the on / off operation of the switch 40, thereby ensuring the subsequent processing using the detected value of the charging current Ic. The filter 55 is provided.

  For example, the filter 55 is configured as a low-pass filter using an average current, a peak detection circuit using a peak current, or a method using a current of a specific phase (sampling hold or synchronous detection at the timing when the switch 40 is turned off). Is possible. FIG. 3 (a) shows an example of a low-pass filter, and FIG. 3 (b) shows an example of a peak detection circuit.

  In addition, when the charging device 10 is operated only in a region where the ripple component of the charging current Ic is small (when the inductance of the coil 42 is sufficiently large compared to the switching period), the filter 55 is omitted. Is possible.

  The charging device 10 includes an AD converter 56 in order to convert the analog signal output from the amplifier 54 into a digital signal.

  As shown in FIG. 1, the charging device 10 further includes an output current detection circuit 57 that detects the output current Is of the solar cell 12.

  The output current detection circuit 57 is a portion of the negative electrode line 22 between the connection point of the negative terminal of the solar cell 12 and the ground point in order to detect the amount of current output from the solar cell 12, that is, the amount of output current Is. And a current detection resistor 58 connected to the. The current detection resistor 58 has a function of converting a current flowing through the solar cell 12 into a voltage.

  The output current detection circuit 57 further includes an amplifier (DC amplifier) 59 that amplifies the voltage of the current detection resistor 58 at a constant magnification. The amplifier 59 outputs an analog signal representing the output current Is of the solar cell 12. The amplifier 59 is configured as a DC linear amplifier, for example.

  As shown in FIG. 1, the charging device 10 further includes a controller 60. The controller 60 is mainly composed of a computer 70 as conceptually shown in a block diagram in FIG. The computer 70 includes a CPU 72, a ROM 74, and a RAM 76 that are connected to each other via a bus 78. The controller 60 further includes an I / O interface 80, and the computer 70 is electrically connected to the AD converter 56 via the I / O interface 80.

  The charging device 10 includes a DA converter 82 in order to convert the digital signal output from the controller 60 into an analog signal. The controller 60 is also electrically connected to the DA converter 82 via the I / O interface 80.

  As shown in FIG. 1, the charging apparatus 10 includes a switch control circuit 84 in order to control the switching operation of the switch 40. The switch control circuit 84 includes a triangular wave source 86, a differential amplifier 87, and a comparator 88. The triangular wave source 86, the differential amplifier 87, and the comparator 88 are all configured as analog circuits that perform calculations at high speed using analog signals.

  The triangular wave source 86 is configured as an oscillator that generates a triangular wave signal having a constant frequency. An example of the oscillator is one in which the oscillation frequency is set to 100 kHz.

  The differential amplifier 87 includes an output voltage of the amplifier 59 (a voltage obtained by converting the output current of the solar battery 12) and an output voltage of the DA converter 82 (a target output current of the solar battery 12 output from the controller 60). A voltage proportional to the difference from the command value) is output. The output voltage of the differential amplifier 87 is input to the comparator 88 as an error signal.

  The differential amplifier 87 shifts to a transient state when the command value of the controller 60 changes and the output voltage of the DA converter 82 changes. In the transient state, the output voltage of the DA converter 82 and the output voltage of the amplifier 59 do not match each other. When these output voltages eventually coincide with each other, the differential amplifier 87 shifts to a steady state. In the steady state, the command value of the controller 60 and the output current of the solar cell 12 match each other.

  The comparator 88 is configured as a voltage comparator that determines a target of two input voltages. The output voltage of the comparator 88 changes to either a high level or a low level in accordance with the magnitude relationship between the two input voltages.

  Specifically, the comparator 88 receives the output voltage of the differential amplifier 87 and the output voltage of the triangular wave source 86, and as a result, the comparator 88 is proportional to the output voltage of the differential amplifier 87. A PWM-generated rectangular wave signal having a pulse width to be output is output. The rectangular wave signal is output to the switch 40 in order to turn the switch 40 on and off. The duty ratio of the switch 40 is determined according to the pulse width of the rectangular wave signal.

  When the command value of the controller 60 changes during the operation of the charging device 10, the output voltage of the differential amplifier 87 changes and the pulse width of the rectangular wave signal of the comparator 88 changes. When the pulse width changes, the duty ratio of the switch 40 changes, and the current output from the solar cell 12 to the capacitor 14 via the switching regulator 32, that is, the charging current Ic of the capacitor 14 changes.

  FIG. 5 shows the triangular wave signal of the triangular wave source 86, the switch command signal supplied to the switch 40, the current flowing through the coil 42, the capacitor 14 and the load 16 in the steady state of the switching regulator 32. Waveforms respectively represented by temporal transitions (represented by Ic) are temporally related to each other and are represented by graphs.

  Specifically, in FIG. 5A, a triangular wave signal having a certain period is represented by a graph together with a threshold voltage signal representing the threshold voltage Vth. The threshold voltage Vth is given by the output voltage of the differential amplifier 87.

  In FIG. 5B, the switch command signal is represented by a graph in association with the ON state and the OFF state of the switch 40. This switch command signal is equal to the rectangular wave signal output from the comparator 88, and the rectangular wave signal is obtained by binarizing the triangular wave signal with a threshold voltage signal. As the threshold voltage Vth increases, the ON pulse width of the switch command signal increases, and as a result, the ON time of the switch 40 becomes longer.

  FIG. 5C is a graph showing how the charging current Ic of the capacitor 14 increases and decreases with the switching operation of the switch 40. The charging current Ic increases during the ON period of the switch 40 and decreases during the OFF period. In a normal state except when the average current of the charging current Ic is small, the current of the coil 42 does not become zero but continues to flow.

  The differential amplifier 87 shown in FIG. 1 operates so that the output voltage of the amplifier 59 matches the output voltage of the DA converter 82. As a result, when the command value of the controller 60 changes, the duty ratio of the switch 40 is changed so that the output voltage of the amplifier 59 matches the output voltage of the DA converter 82. When the output voltage of the amplifier 59 eventually matches the output voltage of the DA converter 82, the duty ratio of the switch 40 is fixed to the value at that time.

  Specifically, when the output current Is of the solar battery 12 increases relative to the current command value of the controller 60, the output voltage of the differential amplifier 87 decreases, and the threshold voltage Vth of the comparator 88 also increases. descend. Then, the duty ratio τ of the switch command signal as a rectangular wave signal supplied from the comparator 88 to the switch 40 decreases, and the switching regulator 32 operates so as to decrease the output current Is of the solar cell 12.

  Conversely, when the output current Is of the solar cell 12 decreases relative to the current command value of the controller 60, the output voltage of the differential amplifier 87 increases and the threshold voltage Vth of the comparator 88 also increases. . Then, the duty ratio τ of the switch command signal as a rectangular wave signal supplied from the comparator 88 to the switch 40 increases, and the switching regulator 32 operates so as to increase the output current Is of the solar cell 12.

  With these two types of operations, the output current Is of the solar cell 12 and the current command value of the controller 60 coincide with each other in a period other than the period in which the charging apparatus 10 is in a transient state.

  As shown in FIG. 1, in the charging device 10, a diode 89 is connected to a portion of the positive line 20 between the connection point with the positive terminal of the capacitor 48 and the external terminal 24. The diode 89 is provided to prevent current from flowing from the capacitor 14 to the solar cell 12 in the reverse direction. When the switch 40 itself has a backflow prevention function, such as when the switch 40 is a bipolar transistor, the diode 89 can be omitted.

  As shown in FIG. 4, the ROM 74 stores various programs including a command value determination program in advance. The command value determination program detects the charging current Ic of the capacitor 14 in a time discrete manner via the charging current detection circuit 50 and determines the command value of the target output current of the solar cell 12 based on the detected value. , Executed by the CPU 72.

  Specifically, the command value determination program determines the value that the output current Is of the solar cell 12 should take in order to substantially maximize the charging current Ic of the capacitor 14 (the controller 60 should output to the differential amplifier 87). In order to determine the current command value) in an exploratory manner by discrete change of the output current Is, it is executed by the CPU 72.

  More specifically, as shown in the time chart of FIG. 6, the command value determination program executes a plurality of subcycles for each search cycle, and increments the current command value for each subcycle. It is executed by the CPU 72 to change only discretely.

  On the other hand, the switch control circuit 84 causes the switch 40 to perform a plurality of switching operations with a common duty ratio τ for each subcycle, as shown in the time chart of FIG.

  In one example, the period of the sub cycle is 10 ms, and the length of one switching operation, that is, the switching period is 10 μs. In this example, the switching operation is performed 1,000 times during one subcycle.

  In this example, the stored energy E of the capacitor 14 is 10 (Wh), and the generated power P of the solar cell 12 is 10 (W). Furthermore, the full charge voltage of the capacitor 14 is 10 (V).

  In this example, since the period of the sub cycle is set to 0.01 seconds, the energy accumulated in the capacitor 14 is equal to one sub cycle (0.01 seconds) if the loss of the charging circuit is ignored. It changes by 0.00028% (= 0.01 seconds ÷ 3600 seconds).

  On the other hand, the stored energy of the capacitor 14 is proportional to the square of the charging voltage Vc of the capacitor 14. Therefore, when the charging voltage Vc changes by 1% with respect to the full charging voltage near the full charging of the capacitor 14, the stored energy of the capacitor 14 changes by 2%. On the other hand, when the charging voltage Vc is around 5 (V), when the charging voltage Vc changes by 1% with respect to the full charging voltage, the accumulated energy of the capacitor 14 changes by 1%.

  Therefore, if the accumulated energy of the capacitor 14 changes by 0.00028% during one subcycle (0.01 seconds), a control error rate of 0.00014% occurs in the charging voltage Vc near full charge. . On the other hand, when the charging voltage is around 5 (V), a control error rate of 0.00028% occurs in the charging voltage Vc.

  Therefore, in the present embodiment, the control error rate γ obtained by dividing the charging voltage Vc of the capacitor 14 by the control error ΔVc of the charging voltage Vc is 0.00028% (0.00014% control error rate and 0 The larger of the control error rates of .0208%).

  Therefore, in this example, the period of the subcycle is set so as not to exceed (E / P) · γ, that is, 0.00028%.

  As shown in FIG. 4, the RAM 76 includes a plurality of memories allocated for storing various digital data. The memories include (a) a command value memory 90 that temporarily stores the determined current command value, and (b) a current current that temporarily stores a current detection value of the charging current Ic by the charging current detection circuit 50. A memory 92; and (c) a previous current memory 94 that temporarily stores a previous detected value of the charging current Ic by the charging current detection circuit 50.

  FIG. 7 conceptually shows a flowchart of the above-described command value determination program. Hereinafter, the current command value determination process in the controller 60 will be described with reference to FIG. 7, but prior to that, the basic principle will be described.

  When the entire system including the charging device 10, the solar battery 12, and the capacitor 14 is operatively in a steady state, the relationship represented by the following expression (1) is established between the solar battery 12 and the capacitor 14. .

  Vs × Is = Vc × Ic

  In the solar cell 12, due to the presence of the capacitor 48, the temporal variation of the generated voltage Vs is small when observed within a time range as short as the subcycle period. Since the temporal variation of the generated voltage Vs is small, the temporal variation of the generated power of the solar cell 12 is also small, and as a result, the temporal variation of the generated current Is of the solar cell 12 is also small.

  On the other hand, in the capacitor 14, the inductance of the coil 42 is normally designed to a value that is large enough to make the direct current component larger than the current change of the coil 42. However, since there is some current fluctuation in the coil 42, the current flowing through the coil 42 is a ripple current. On the other hand, the capacitance of the capacitor 14 has such a large value that the charging voltage Vc of the capacitor 14 does not change in a short time.

  The instantaneous value of the electric energy flowing into the capacitor 14 is represented by the product of the charging voltage Vc and the charging current Ic. As described above, the charging voltage Vc of the capacitor 14 is substantially constant when observed within a short time range. Therefore, the amount of electric energy flowing into the capacitor 14 is proportional to the current flowing into the capacitor 14, that is, the charging current Ic.

  Therefore, within a short time range, the determination of whether the electric energy flowing into the capacitor 14 is large or small is sufficient by determining whether the charging current Ic is large or small without considering the charging voltage Vc of the capacitor 14. Can be done accurately.

  By the way, if the switching period of the switch 40 is represented by T, the on time is represented by Ton, and the off time is represented by Toff, the relationship represented by the following equation (2) is established among these three members.

  T = Ton + Toff

  The duty ratio τ of the switch 40 is expressed by the following equation (3).

  τ = Ton / T

  When the duty ratio τ of the switch 40 is determined, the relationship expressed by the following equation (4) is approximately established between the power generation voltage Vs of the solar cell 12 and the charging voltage Vc of the capacitor 14.

  (Vs−Vc) ÷ L × Ton≈Vc ÷ L × Toff = Vc ÷ L × (T-Ton)

  In this equation, “L” represents the inductance value of the coil 42. In this equation, the left side means an increase in the current of the coil 42 when the switch 40 is in the on state, while the right side means a decrease in the current of the coil 42 when the switch 40 is in the off state. From this equation, the following equations (5) to (7) are derived.

  Vs × Ton = Vc × T

  Ton / T = Vc / Vs

  Ton / T = Is / Ic

  Due to the characteristics of the capacitor 14 described above, the charging voltage Vc of the capacitor 14 does not change sensitively. On the other hand, the power generation voltage Vs of the solar cell 12 can change within the voltage range represented by the characteristic curve shown in FIG. Thus, since the charging voltage Vc of the capacitor 14 does not change within a short time range, when the duty ratio τ of the switch 40 is changed, the power generation voltage Vs of the solar cell 12 changes. Immediately after the change of the duty ratio τ, the switching regulator 32 is in a transient state, but eventually the generated voltage Vs of the solar cell 12 converges to a value represented by the following equation (8).

  Vs = Vc × T ÷ Ton

  When the power generation voltage Vs of the solar cell 12 changes in this way, the power generation current Is of the solar cell 12 also changes. The generated current Is after the change is determined according to the characteristic curve of the solar cell 12 and the illuminance of sunlight at that time.

  When the power generation voltage Vs and the power generation current Is of the solar battery 12 change in this way, the power generation of the solar battery 12 also changes. If the generated power of the solar cell 12 changes, the charging power of the capacitor 14 also changes, and the change is reflected only in the charging current Ic, not in the charging voltage Vc of the capacitor 14.

  FIG. 8 shows the change indicated by the charging current Ic of the capacitor 14 when the command value of the output current Is of the solar cell 12 (duty ratio τ of the switch 40) is changed under the condition that the illuminance of sunlight is constant. An example is shown in a graph.

  As described above, because the generated power of the solar cell 12 has a maximum value with respect to the generated voltage Vs and the generated current Is, the charging power of the capacitor 14 also has a maximum value. On the other hand, in the capacitor 14, as described above, within a short time range, the charging voltage Vc does not change with time, whereas the charging current Ic is variable. Therefore, the phenomenon that the generated power of the solar cell 12 has a maximum value is observed as a phenomenon in which the charging current Ic of the capacitor 14 has a maximum value.

  Therefore, if the command value of the output current Is continues to increase from the value corresponding to the point A in FIG. 8, the charging current Ic continues to decrease, whereas if the command value of the output current Is continues to decrease from the value corresponding to the point A, the charging current After Ic increases and reaches the maximum value, it starts to decrease.

  On the other hand, if the command value of the output current Is continues to decrease from the value corresponding to the point B in FIG. 8, the charging current Ic continues to decrease, whereas if the command value continues to increase from the value corresponding to the point B, the charging current After Ic increases and reaches the maximum value, it starts to decrease.

  Therefore, the optimum value of the command value of the output current Is, that is, the value corresponding to the maximum value of the charging current Ic can be determined in an exploratory manner by changing the command value of the output current Is.

  Based on the knowledge described above, in the command value determination program shown in FIG. 7, generally, in order to exploratively determine the optimum value of the output current Is of the solar cell 12, the command value of the output current Is (current A sub-cycle in which the command value) Id is changed discretely, that is, in a stepwise manner under a predetermined condition is repeated in a time discrete manner.

  In each subcycle, the change condition (whether to increase or decrease) of the current command value Id in the next subcycle is determined according to the response of the charging current Ic of the capacitor 14 to the discrete change of the current command value Id. The These multiple subcycles are repeated until the charging current Ic of the capacitor 14 is substantially maximized.

  Further, in each sub-cycle, the previous detection value that is the charging current Ic detected by the charging current detection circuit 50 before the current discrete change is performed, and the charge current detection after the current discrete change is performed. The current detection value that is the charging current Ic detected by the circuit 50 is compared with each other.

  Using the comparison result, the response of the charging current Ic of the capacitor 14 to the current discrete change of the current command value Id is monitored. As will be described later, one sub-cycle is a measurement of the charging current Ic, determination of a current command value, and a series of duty ratio control of the switch 40 (that is, a switching operation of a plurality of setting times, and a waiting time Tf described later). Is continued for an equal period of time). However, the series of duty ratio control is executed by the switch control circuit 84.

  Here, the command value determination program will be specifically described with reference to FIG. 7. When the command value determination program is executed by the CPU 72, first, in S100, the current value Id1 of the current command value Id is initialized. It is set as a value I0 and stored in the command value memory 90. The initial value I0 can be set to 0 (A), for example.

  Next, in S110, it is waited for a certain waiting time Tf to elapse. The length of the waiting time Tf (for example, 10 ms) is set so as not to be shorter than the time required for the switching regulator 32 to settle after the transition to the transient state because the current command value Id is changed stepwise. Is done. The length of the waiting time Tf is set in consideration of the time constant of the capacitor 14 and the coil 42 (for example, the time constant of the LC filter described above).

  If the waiting time Tf is set to 10 ms and the switching period T of the switch 40 is set to 10 μs, the sub-cycle period is approximately 10 ms, and the switching operation (minimum unit of on / off control) of the switch 40 is 1 during that period. 1,000 times. If a switching operation of this length is performed, it is expected that the transient phenomenon of the entire circuit due to the step change of the current command value Id will converge well.

  The switch control circuit 40 continues to control the duty ratio of the switch 40 for a time equal to the waiting time Tf.

  Subsequently, in S120, the current value of the charging current Ic of the capacitor 14 is measured as the previous current ia through the charging current detection circuit 50. The measured previous current ia is stored in the previous current memory 94. Thereafter, in S130, the current value of the step size ΔI of the current command value Id is set to be equal to the initial value ΔI0 (this time is equal to the default value).

  Subsequently, the maximum value of the charging current Ic is searched by increasing the current command value Id by the increment ΔI and monitoring the response appearing in the charging current Ic of the capacitor 14.

  Specifically, in S200, the current value Id1 of the current command value Id is updated so as to increase by the current value of the step width ΔI (this time is equal to the initial value ΔI0). The updated value Id2 is stored in the command value memory 90 and is supplied from the computer 70 to the switch control circuit 84 via the DA converter 82. When the update value Id2 is supplied, the switch control circuit 84 controls the duty ratio τ of the switch 40 so that the output current Is of the solar cell 12 becomes equal to the update value Id2.

  Subsequently, in S210, it is waited for the waiting time Tf to elapse. The switch control circuit 40 continues to control the duty ratio of the switch 40 for a time equal to the waiting time Tf.

  Thereafter, in S220, the current value of the charging current Ic of the capacitor 14 is measured as the current current ib through the charging current detection circuit 50. The measured current current ib is stored in the current current memory 92.

  Subsequently, in S230, it is determined whether or not the current current ib is smaller than the previous current ia. That is, it is determined whether or not the charging current Ic has decreased with respect to the step increase of the current command value Id.

  If it is assumed that the current current ib is smaller than the previous current ia this time, the determination in S230 is YES, and in S240, the step size ΔI corresponds to the content of the response of the charging current Ic to the temporal change in the current command value Id. Flexible.

  Specifically, the next value of the step size ΔI is determined by doubling the absolute value of the current value of the step size ΔI and inverting the sign thereof. More specifically, the next value of the step size ΔI is calculated by multiplying the value obtained by subtracting the previous value Id1 from the current value Id2 of the current command value Id by “−2”.

  In FIGS. 9A and 9B, two examples of changes in the charging current Ic with respect to the current command value Id are respectively represented by graphs.

  FIG. 9A shows an example in which the charging current Ic decreases with a discrete increase in the current command value Id. In this example, by executing the above-described S240, the line segment between the plot point A of the previous value ia and the plot point B of the current value ib of the charging current ic is 1: 1 and from the plot point B to the plot point A. The next value ΔInx of the step size ΔI necessary to determine the next value of the current command value Id is determined so that the plot point C of the next value ic of the charging current ic is located at a point that is divided externally.

  In the example shown in FIG. 9A, the next value ΔInxt of the step size ΔI is calculated as −2 (Id2-Id1). Therefore, the next value of the current command value Id is calculated using the following formula: Id2 + ΔInxt = Id2-2 (Id2-Id1) = 2 × Id1-Id2.

  Thereafter, in S250 of FIG. 7, the previous value Id1 of the current command value Id is updated to be equal to the current value Id2 in preparation for the next execution of S200. Thereafter, in S260, the previous current ia is updated to be equal to the current current ib in preparation for the next execution of S230. Subsequently, returning to S200, the current value Id2 of the current command value Id is calculated by addition to the latest step size ΔI.

  On the other hand, assuming that the current current ib is larger than the previous current ia this time, the determination in S230 is NO, and in S270, it is determined whether or not the current current ib is larger than the previous current ia. The determination in S270 is YES based on the above assumption, and the process proceeds to S280.

  In S280, the step size ΔI is determined flexibly according to the content of the response of the charging current Ic to the temporal change in the current command value Id.

  Specifically, the next value of the step width ΔI is determined so as to be equal to the current value of the step width ΔI. More specifically, the next value of the step width ΔI is calculated so as to be equal to the value obtained by subtracting the previous value Id1 from the current value Id2 of the current command value Id.

  FIG. 9B shows an example in which the charging current Ic increases with a discrete increase in the current command value Id. In this example, by executing the above-described S280, the line segment between the plot point A of the previous value ia and the plot point B of the current value ib of the charging current ic is 1: 1 and from the plot point A to the plot point B. The next value ΔInx of the step size ΔI necessary to determine the next value of the current command value Id is determined so that the plot point C of the next value ic of the charging current ic is located at a point that is divided externally.

  In the example shown in FIG. 9B, the next value ΔInxt of the step size ΔI is calculated as + (Id2−Id1). Therefore, the next value of the current command value Id is calculated using the following formula: Id2 + ΔInxt = Id2 + (Id2-Id1) = 2 × Id2-Id1.

  Thereafter, the process proceeds to S250 in FIG. In preparation for the next execution of S200, the previous value Id1 of the current command value Id is updated to be equal to the current value Id2. Thereafter, in S260, the previous current ia is updated to be equal to the current current ib in preparation for the next execution of S230. Subsequently, returning to S200, the current value Id2 of the current command value Id is calculated by addition to the latest step size ΔI.

  If it is assumed that the current current ib is substantially equal to the previous current ia (the difference between the two is equal to or less than the allowable value) this time, both the determination in S230 and the determination in S270 are NO, and the current search cycle ends. Thereafter, in S290, the initial value I0 is set to be equal to the current value Id2 of the current command value Id in preparation for the next execution of S100.

  Thereafter, in S300, it is determined whether a condition for resuming the search cycle is satisfied.

  For example, if the next search cycle is not started until the set time has elapsed since the end of the previous search cycle, whether or not the set time has elapsed since the end of the previous search cycle is determined in S300. Determined. Further, when the next search cycle is started when the current value of the charging current Ic changes more than the allowable value from the value at the end of the previous search cycle, in this S300, the current value of the charging current Ic It is determined whether the value has changed by more than an allowable value from the value at the end of the previous search cycle.

  In any case, if the condition for resuming the search cycle is satisfied, the determination in S300 is YES, the process returns to S100, and a new search cycle is started.

  In the present embodiment, when the execution of the command value determination program is started in a state where the initial value I0 is 0 (A), the operating point of the solar cell 12, that is, as shown in FIG. The plot point on the graph moves from point E to point B, and further moves from point B to point A for optimization.

  In the present embodiment, the optimization control of the output current Is of the solar cell 12 is started from a state where the current command value Id is 0. This is because the optimization control is performed when the output voltage Vs of the solar cell 12 is It means that the tendency to be performed in a high region becomes strong. On the other hand, the electric power necessary for the operation of the charging device 10 is supplied from the solar battery 12.

  Therefore, according to this embodiment, it becomes possible to operate the charging device 10 effectively using the high voltage of the solar cell 12.

  As is apparent from the above description, in the present embodiment, the switch control circuit 84 constitutes an example of the “duty ratio control unit” in the item (1), and the AD converter 56, the controller 60, and the DA The converters 82 cooperate with each other to constitute an example of the “command value supply unit” in the same section.

  Furthermore, in the present embodiment, the portion of the controller 60 that executes S230, S240, S270, and S280 in FIG. 7 constitutes an example of the “first determining unit” in the above section (5). The part that executes S200 in the figure constitutes an example of the “second determining unit” in the same section.

  Next, a second embodiment of the present invention will be described. However, this embodiment differs from the first embodiment only in the software configuration related to command value determination, and the other software configuration and hardware configuration are common, so only the different parts will be described in detail and shared. The part which performs is quoted using the same code | symbol or name, and the duplicate description is abbreviate | omitted.

  In the first embodiment, the command value Id of the output current Is of the solar cell 12 is discretely changed so that the charging current Ic of the capacitor 14 is substantially maximized, whereby the optimum value of the output current Is is reached. Is determined exploratoryly.

  On the other hand, in this embodiment, the command value Vd of the output voltage Vs of the solar cell 12 is discretely changed so that the charging current Ic of the capacitor 14 is substantially maximized, whereby the output voltage Vs. Is optimally determined.

  FIG. 10 shows a charging device 200 according to the present embodiment in the same manner as FIG. The charging apparatus 200 shown in FIG. 10 has many elements common to the charging apparatus 10 shown in FIG. 1 with respect to the hardware configuration, and only the elements for monitoring the power generation state of the solar cell 12 are different.

  Specifically, in the charging apparatus 200, an output voltage detection circuit 202 that detects the output voltage Vs of the solar battery 12 is provided instead of the output current detection circuit 57 shown in FIG. The output voltage detection circuit 202 is connected to the positive electrode line 20 that is equipotential with the output voltage Vs of the solar battery 12 and one input terminal of the differential amplifier 87. In the present embodiment, the output voltage detection circuit 202 is configured as a simple conductor, but necessary changes can be made.

  Unlike the controller 60 shown in FIG. 1, the controller 60 shown in FIG. 10 determines a command value for the output voltage Vs of the solar battery 12 and outputs a digital signal representing the determined command value (voltage command value) Vd. -Output to A converter 82. The DA converter 82 outputs an analog signal representing the voltage command value Vd to the other input terminal of the differential amplifier 87.

  The differential amplifier 87 determines the difference between the output voltage Vs of the solar battery 12 and the output voltage of the DA converter 82 (the voltage representing the command value Vd of the output voltage Vs of the solar battery 12 output from the controller 60). Outputs a proportional voltage. The differential amplifier 87 operates so that the voltage command value Vd and the output voltage Vs of the solar battery 12 coincide with each other.

  FIG. 11 conceptually shows a command value determination program executed by the computer 70 of the controller 60 shown in FIG. 10 in a flowchart. The command value determination program is stored in the ROM 74.

  The command value determination program will be described below with reference to FIG. However, this command value determination program is different from the command value determination program shown in FIG. 7 in that the output current Is is replaced with the output voltage Vs and the current command value Id is replaced with the voltage command value Vd. The common steps are simply described.

  When the command value determination program is executed by the CPU 72, first, in S500, the current value Vd1 of the voltage command value Vd is set as the initial value V0 in accordance with S100.

  Similarly to the charging device 10, the charging device 200 is also supplied with electric power from the solar cell 12 and operates. Therefore, if the initial value V0 is too close to 0, it is difficult to effectively operate the charging device 200 by the solar battery 12. Therefore, the initial value V0 is not 0 (V) but can be set to be equal to the product of the maximum output voltage of the solar cell 12 and a value within a range from about 1/2 to about 1/4. desirable.

  Next, in S510, it is waited for the waiting time Tf to elapse as in S110. Subsequently, in S520, the current value of the charging current Ic of the capacitor 14 is measured as the previous current ia through the charging current detection circuit 50, as in S120. Thereafter, in S530, in accordance with S130, the current value of the increment ΔV of the voltage command value Vd is set to be equal to the initial value ΔV0 (this time is equal to the default value).

  Thereafter, in S600, in accordance with S200, the current value Vd1 of the voltage command value Vd is updated so as to increase by the current value of the step width ΔV (this time is equal to the initial value ΔV0). Subsequently, in S610, it is waited for the waiting time Tf to elapse as in S210. Thereafter, in S620, as in S220, the current value of the charging current Ic of the capacitor 14 is measured as the current current ib through the charging current detection circuit 50.

  Subsequently, in S630, as in S230, it is determined whether or not the current current ib is smaller than the previous current ia. If it is assumed that the current current ib is smaller than the previous current ia this time, the determination in S630 is YES, and in S640, the current value Vd1 is subtracted from the current value Vd2 of the voltage command value Vd according to S240. -2 "is multiplied to calculate the next step value ΔV.

  Thereafter, in S650, in accordance with S250, the previous value Vd1 of the voltage command value Vd is updated to be equal to the current value Vd2 in preparation for the next execution of S600. Thereafter, in S660, as in S260, the previous current ia is updated to be equal to the current current ib in preparation for the next execution of S630. Subsequently, returning to S600, the current value Vd2 of the voltage command value Vd is calculated by addition to the latest step size ΔV.

  On the other hand, this time, assuming that the current current ib is larger than the previous current ia, the determination in S630 is NO, and in S670, it is determined whether the current current ib is larger than the previous current ia as in S270. The The determination in S670 is YES based on the above assumption, and the process proceeds to S680.

  In S680, in accordance with S280, the next value of the step size ΔV is calculated so as to be equal to the value obtained by subtracting the previous value Vd1 from the current value Vd2 of the voltage command value Vd. Thereafter, the process proceeds to S650.

  This time, assuming that the current current ib is substantially equal to the previous current ia (the difference between them is equal to or less than the allowable value), both the determination in S630 and the determination in S670 are NO, and the current search cycle ends. Thereafter, in S690, in accordance with S290, the initial value V0 is set to be equal to the current value Vd2 of the voltage command value Vd in preparation for the next execution of S500.

  Thereafter, in S700, as in S300, it is determined whether a condition for restarting the search cycle is satisfied. If the condition for resuming the search cycle is satisfied, the determination in S700 is YES, the process returns to S500, and a new search cycle is started.

  In the present embodiment, when the execution of the command value determination program is started in a state where the initial value V0 is 0 (V), the operating point of the solar cell 12, that is, as shown in FIG. The plot point on the graph moves from point D to point C, and further moves from point C to point A for optimization.

  In the present embodiment, such optimization control is started from a state in which the voltage command value Vd is close to 0. This is because the optimization control is performed when the output current Is of the solar cell 12 is large. It means that the tendency to be done in the area becomes stronger.

  As is clear from the above description, in the present embodiment, the switch control circuit 84 constitutes an example of the “duty ratio control unit” in the item (10), and the AD converter 56, the controller 60, and the DA The converters 82 cooperate with each other to constitute an example of the “command value supply unit” in the same section.

  Further, in the present embodiment, the portion of the controller 60 that executes S630, S640, S670, and S680 in FIG. 11 constitutes an example of the “first determination unit” in the above item (12). The part that executes S600 in the figure constitutes an example of the “second determining unit” in the same section.

  Next, a third embodiment of the present invention will be described. However, this embodiment differs from the first embodiment only in the software configuration related to command value determination, and the other software configuration and hardware configuration are common, so only the different parts will be described in detail and shared. The part which performs is quoted using the same code | symbol or name, and the duplicate description is abbreviate | omitted.

  In general, in the switching regulator 32, when the duty ratio of the switch 40 is 100%, that is, when the switch 40 continues to be turned on in one switching cycle, the power conversion action of the switching regulator 32 (based on the inductance of the coil 42). The phenomenon in which an electromotive force is induced in the circuit due to a change in the current flowing in the circuit of the charging device 10 is not performed.

  In the first embodiment, the switch 40 is controlled so as to extract output energy from the solar cell 12 exceeding the power generation capacity of the solar cell 12 according to the amount of solar radiation, that is, the output current Is of the solar cell 12 is When the switch 40 is controlled to be larger than the actual power generation capacity of the solar cell 12, the duty ratio of the switch 40 becomes 100%.

  When the power conversion action of the switching regulator 32 is not performed, the current and the voltage between the solar cell 12 and the capacitor 16 become equal to each other, and as a result, the optimum for the charging current Ic of the capacitor 14 to be substantially maximized. Neither the output current Is nor the output voltage Vs of the solar cell 12 can be controlled.

  In other words, if it is detected that the output current Is of the solar cell 12 and the charging current Ic of the capacitor 14 are equal to each other, the duty ratio of the switch 40 becomes 100%, and a state where control is impossible is detected. Can do.

  In the first embodiment, a signal representing the output current Is of the solar cell 12 is not input to the controller 60. Therefore, the output current Is and the charging current Ic cannot be directly compared with each other.

  However, by detecting that the charging current Ic of the capacitor 14 has become smaller than the current command value Id to the solar battery 12, it can be detected that the duty ratio of the switch 40 has become 100%. The reason will be specifically described below.

  When the current command value Id gradually increases from 0, the output current Is also increases. Meanwhile, the current command value Id and the output current Is coincide with each other. As the output current Is increases, the charging current Ic of the capacitor 14 also increases. Meanwhile, the duty ratio of the switch 40 also increases.

  When the current command value Id further increases, the duty ratio of the switch 40 eventually reaches 100%. At that time, the output current Is and the charging current Ic coincide with each other, and the output current Is and the charging current Ic when the duty ratio of the switch 40 is 100% are both expressed as the maximum current Imax.

  Since neither the output current Is nor the charging current Ic can exceed the maximum current Imax, when the current command value Id is determined to be larger than the maximum current Imax, the current command value Id is the maximum current Imax, that is, the output current Is. A state larger than the actual value and the actual value of the charging current Ic is realized.

  Therefore, by detecting that the charging current Ic of the capacitor 14 is smaller than the current command value Id, it can be detected that the duty ratio of the switch 40 has reached 100%.

  On the other hand, the power conversion action of the switching regulator 32 is smaller as the current difference that is the difference between the output current Is of the solar cell 12 and the charging current Ic of the capacitor 14 is smaller. That is, the smaller the current difference, the closer the power conversion action of the switching regulator 32 approaches its limit.

  Based on the knowledge described above, in charging device 10 according to the present embodiment, in each sub-cycle, a current difference that is a difference between output current Is of solar cell 12 and charging current Ic of capacitor 14 in the previous sub-cycle is obtained. The step size ΔI of the current command value Id is determined so as to decrease as the value decreases.

  Therefore, according to the charging device 10, the power conversion action of the switching regulator 32 is not performed due to the switch 40 being kept on. As a result, the output current Is of the solar cell 12 is also the charging current Ic of the capacitor 14. Can be avoided from being optimized.

  FIG. 12 conceptually shows a command value determination program executed by the computer 70 of the controller 60 shown in FIG. 1 in a flowchart. The command value determination program is stored in the ROM 74.

  Hereinafter, this command value determination program will be described with reference to FIG. However, this command value determination program will be briefly described by quoting steps common to the command value determination program shown in FIG. 7 using the same step numbers.

  When this command value determination program is executed by the CPU 72, first, in S100, the current value Id1 of the current command value Id is set as the initial value I0. Next, in S110, it is waited for the waiting time Tf to elapse.

  Subsequently, in S120, the current value of the charging current Ic of the capacitor 14 is measured as the previous current ia through the charging current detection circuit 50. Thereafter, in S130, the current value of the step size ΔI of the current command value Id is set to be equal to the initial value ΔI0 (this time is equal to the default value).

  Thereafter, in S200, the current value Id1 of the current command value Id is updated so as to increase by the current value of the step width ΔI (this time is equal to the initial value ΔI0), and this is set as the current value Id2. Subsequently, in S210, it is waited for the waiting time Tf to elapse. Thereafter, in S220, the current value of the charging current Ic of the capacitor 14 is measured as the current current ib through the charging current detection circuit 50.

  Subsequently, in S221, it is determined whether or not the absolute value of the previous current difference, which is the difference between the previous current ia and the previous value Id1, is larger than the reference value A. If it is assumed that the absolute value of the previous current difference is not larger than the reference value A this time, the determination in S221 is NO and the process proceeds to S222.

  In S222, it is determined whether or not the absolute value of the current current difference, which is the difference between the current current ib and the current value Id2, is greater than the reference value A. This time, assuming that the absolute value of the current difference is not larger than the reference value A, the determination in S222 is NO, and the process proceeds to S223.

  In S223, a coefficient K described in detail later is set as the coefficient K1. On the other hand, since either the previous current difference or the current current difference is larger than the reference value A, the determination in S221 is YES, or the determination in S221 is NO, but the determination in S222 is YES. In S224, the coefficient K is set as a coefficient K0 that is larger than the coefficient K1. The coefficient K0 can be set to “1”, and the coefficient K1 can be set to a numerical value smaller than “1” (for example, 1/10 of the coefficient K0).

  Subsequently, in S230, it is determined whether or not the current current ib is smaller than the previous current ia. If it is assumed that the current current ib is smaller than the previous current ia this time, the determination in S230 is YES, and in S241, the value obtained by subtracting the previous value Id1 from the current value Id2 of the current command value Id is set to (−2). By multiplying the product with K, the next value of the step size ΔI is calculated.

  Therefore, according to the present embodiment, the step width ΔI is calculated such that the smaller the previous current difference and the current current difference, the smaller the absolute value of the step width ΔI.

  Thereafter, in S250, the previous value Id1 of the current command value Id is updated to be equal to the current value Id2 in preparation for the next execution of S200. Thereafter, in S260, the previous current ia is updated to be equal to the current current ib in preparation for the next execution of S230. Subsequently, returning to S200, the current value Id2 of the current command value Id is calculated by addition to the latest step size ΔI.

  On the other hand, assuming that the current current ib is larger than the previous current ia this time, the determination in S230 is NO, and in S270, it is determined whether or not the current current ib is larger than the previous current ia. The determination in S270 is YES based on the above assumption, and the process proceeds to S281.

  In S281, the next value of the step size ΔI is calculated so as to be equal to the product of the value Kd obtained by subtracting the previous value Id1 from the current value Id2 of the current command value Id. Thereafter, the process proceeds to S250.

  Therefore, according to the present embodiment, the step width ΔI is calculated such that the smaller the previous current difference and the current current difference, the smaller the absolute value of the step width ΔI.

  This time, assuming that the current current ib is substantially equal to the previous current ia (the difference between the two is equal to or less than the allowable value), both the determination at S230 and the determination at 2670 are NO, and the current search cycle ends. Thereafter, in S290, the initial value I0 is set to be equal to the current value Id2 of the current command value Id in preparation for the next execution of S100.

  Thereafter, in S300, it is determined whether a condition for resuming the search cycle is satisfied. If the condition for resuming the search cycle is satisfied, the determination in S700 is YES, the process returns to S100, and a new search cycle is started.

  FIG. 13 is a graph showing an example of how the coefficient K changes with time during one search cycle. In this example, when one search cycle is started, the coefficient K is first set to a coefficient K0 (for example, “1”) for setting the coarse step size ΔI. In this example, since the current difference becomes smaller than the reference value A after a plurality of sub-cycles are repeated using this coefficient K0, the coefficient K is a coefficient K1 for setting a fine step size ΔI ( For example, “0.1”).

  In addition, in this embodiment, the next value of the step size ΔI is obtained by multiplying the value estimated from the current value Id2 and the previous value Id1 of the current command value Id by a coefficient corresponding to the current difference. Although calculated, it can be determined to change only in accordance with the current difference.

  For example, when a candidate step size ΔIL and a smaller candidate step size ΔIS are set in advance and the current difference is larger than the reference value A, the coarse candidate step size ΔIL is determined as the step size ΔI, while the current difference is If it is not larger than the reference value A, the present invention can be implemented in such a manner that the fine candidate step size ΔIS is determined as the step size ΔI.

  This aspect can be implemented by setting the candidate step sizes ΔIL and ΔIS to, for example, 10% and 1% of the maximum output current of the solar cell 12, respectively. In this case, after the subcycle with the coarse candidate step size ΔIL is repeated about 10 times, the subcycle with the fine step size ΔIS is repeated about 10 times. As a result, the actual value of the charging current Ic of the capacitor 14 is The optimal value may be reached with an error range of 1% with respect to the true maximum value.

  As is apparent from the above description, in this embodiment, the portion of the controller 60 that executes S221 to S224, S230, S241, S270, and S281 in FIG. It constitutes an example of a “width determining unit”.

  Next, a fourth embodiment of the present invention will be described. However, this embodiment differs from the first embodiment only in the software configuration related to command value determination, and the other software configuration and hardware configuration are common, so only the different parts will be described in detail and shared. The part which performs is quoted using the same code | symbol or name, and the duplicate description is abbreviate | omitted.

  In the first embodiment, the absolute value of the step size ΔI does not change during one search cycle. That is, whether the actual value of the charging current Ic of the capacitor 14 has just begun to approach the maximum value that is the optimum value (whether it is the beginning of the optimization control of the output current Is of the solar cell 12) or soon. The current command value Id is determined using the step size ΔI having the same absolute value regardless of whether it reaches (optimization control is about to end).

  By the way, in an environment where the absolute value of the step size ΔI does not change during one search cycle, setting the absolute value of the step size ΔI to a large value is necessary for the actual value of the charging current Ic to approach the optimum value. Time can be shortened, whereby the speed of optimization control can be easily increased. On the other hand, however, since the step size ΔI is coarse, there is a possibility that the possibility that it becomes difficult to make the actual value of the charging current Ic coincide with the true optimum value sufficiently accurately may increase.

  On the other hand, when the absolute value of the step width ΔI is set to a small value, since the step size ΔI is fine, the actual value of the charging current Ic can be easily matched with the true optimum value with sufficient accuracy. can get. However, on the other hand, since the step size ΔI is small, the time required for the actual value of the charging current Ic to approach the optimum value becomes long, thereby making it difficult to speed up the optimization control. there is a possibility.

  On the other hand, during one search cycle, as shown in FIG. 2, the rate of change of the output voltage Vs with respect to the output current Is of the solar cell 12 increases as the output power of the solar cell 12 approaches its maximum value. To do.

  This means that as the charging power of the capacitor 14 approaches its maximum value, the current change rate, which is the change rate of the charging current Ic with respect to the output current Is of the solar cell 12, increases. If attention is paid to the fact that the charging voltage Vc of the capacitor 14 is substantially constant during one sub-cycle, the current change rate increases as the charging current Ic of the capacitor 14 approaches its maximum value. Means to increase.

  On the other hand, while the charging current Ic of the capacitor 14 is away from its maximum value, the output current Is of the solar cell 12 is repeatedly changed discretely with a coarse step size ΔI, while the charging of the capacitor 14 is repeated. During a period in which the current Ic is sufficiently close to its maximum value, it is possible to repeatedly change the output current Is of the solar cell 12 with a small step size ΔI to speed up the optimization control of the output current Is. It is desirable to achieve both high performance and high accuracy.

  In view of the knowledge described above, in the present embodiment, while the current change rate is small, it is possible to repeatedly change the output current Is of the solar cell 12 with a coarse step size ΔI while repeating the above. During the period in which the current change rate is large, the output current Is of the solar cell 12 can be changed discretely with a small step size ΔI.

  FIG. 14 conceptually shows a command value determination program executed by the computer 70 of the controller 60 shown in FIG. 1 in a flowchart. The command value determination program is stored in the ROM 74.

  Hereinafter, this command value determination program will be described with reference to FIG. However, this command value determination program will be briefly described by quoting steps common to the command value determination program shown in FIG. 7 using the same step numbers.

  When this command value determination program is executed by the CPU 72, first, in S100, the current value Id1 of the current command value Id is set as the initial value I0. Next, in S110, it is waited for the waiting time Tf to elapse. Subsequently, in S120, the current value of the charging current Ic of the capacitor 14 is measured as the previous current ia through the charging current detection circuit 50. Thereafter, in S130, the current value of the step size ΔI of the current command value Id is set to be equal to the initial value ΔI0 (this time is equal to the default value).

  Thereafter, in S200, the current value Id1 of the current command value Id is updated so as to increase by the current value of the step width ΔI (this time is equal to the initial value ΔI0), and this is set as the current value Id2. Subsequently, in S210, it is waited for the waiting time Tf to elapse. Thereafter, in S220, the current value of the charging current Ic of the capacitor 14 is measured as the current current ib through the charging current detection circuit 50.

  Subsequently, in S225, the rate of change of the charging current Ic with respect to the output current Is is calculated as the current rate of change γ. The current change rate γ is calculated, for example, by dividing the change amount of the charging current Ic (= current current ib−previous current ia) by the change amount of the current command value Id (= current value Id2−previous value Id1). Is done.

  Thereafter, in S227, the current value of the step width ΔI is determined according to the calculated current change rate γ. Specifically, data (for example, a function formula, a table, etc.) for defining the relationship between the two so that the step size ΔI decreases according to the current change rate γ is stored in advance in the ROM 74, and the data is referred to. Thus, the current value of the step width ΔI corresponding to the current value of the current change rate γ is determined.

  FIG. 15 is a graph showing an example of the relationship between the current change rate γ and the step size ΔI. In this example, when the current change rate γ is within the range of 0 and the reference value γ0, the step size ΔI is determined to be equal to the initial value ΔI0. As the current change rate γ increases from the reference value γ0, the step size ΔI is determined to decrease from the initial value ΔI0. The step width ΔI is maintained at the minimum value ΔImin after reaching the minimum value ΔImin regardless of the increase in the current change rate γ. As a result, the step size ΔI is changed between the initial value ΔI0 and the minimum value ΔImin greater than zero.

  Subsequently, in S230, it is determined whether or not the current current ib is smaller than the previous current ia. If it is assumed that the current current ib is smaller than the previous current ia this time, the determination in S230 is YES. In S242, the next value of the step size ΔI is equal to the step size ΔI determined in S227. Are determined to be the opposite. That is, in S242, the next value of the step width ΔI is determined by inverting the sign of the step width ΔI determined in S227.

  Thereafter, in S250, the previous value Id1 of the current command value Id is updated to be equal to the current value Id2 in preparation for the next execution of S200. Thereafter, in S260, the previous current ia is updated to be equal to the current current ib in preparation for the next execution of S230. Subsequently, returning to S200, the current value Id2 of the current command value Id is calculated by addition to the latest step size ΔI.

  On the other hand, assuming that the current current ib is larger than the previous current ia this time, the determination in S230 is NO, and in S270, it is determined whether or not the current current ib is larger than the previous current ia. The determination in S270 is YES based on the above assumption, and the process proceeds to S282.

  In S282, the next value of the step width ΔI is determined so that the step width ΔI determined in S227 is equal to the absolute value and the sign. That is, in S282, the step width ΔI determined in S227 is determined as it is as the next value of the step width ΔI. Thereafter, the process proceeds to S250.

  If it is assumed that the current current ib is substantially equal to the previous current ia (the difference between the two is equal to or less than the allowable value) this time, both the determination in S230 and the determination in S270 are NO, and the current search cycle ends. Thereafter, in S290, the initial value I0 is set to be equal to the current value Id2 of the current command value Id in preparation for the next execution of S100.

  Thereafter, in S300, it is determined whether a condition for resuming the search cycle is satisfied. If the condition for resuming the search cycle is satisfied, the determination in S700 is YES, the process returns to S100, and a new search cycle is started.

  In FIGS. 16A and 16B, the characteristics of the solar cell 12 are shown in graphs for the case where the amount of sunlight received by the solar cell 12 is large and the case where the amount of sunlight is small. In any case, as the output power of the solar cell 12 approaches its maximum value, the rate of change of the output voltage Vs with respect to the output current Is of the solar cell 12 increases. As apparent from FIGS. 16A and 16B, the optimum value of the output current Is of the solar cell 12 varies depending on the amount of sunlight received by the solar cell 12. Generally, the smaller the amount of sunlight, the optimum value. Decrease.

  Therefore, even if the step width ΔI is changed in accordance with the degree of control of the output current Is, if the change pattern of the step width ΔI does not depend on the amount of sunlight, it is apparent from FIGS. 16 (a) and 16 (b). For example, when the amount of sunshine is large, the control of the output current Is is performed with a small step size ΔI in the vicinity of the true optimum value, but when the amount of sunshine is small, the control of the output current Is is performed. There is a possibility that the fine step size ΔI is not performed in the vicinity of the true optimum value.

  On the other hand, according to the present embodiment, since the step width ΔI is changed according to the current change rate, the change pattern of the step width ΔI is performed so as to reflect the amount of sunlight. As a result, regardless of the amount of sunlight, it is guaranteed that the control of the output current Is with a small step size ΔI is performed in the vicinity of the true optimum value.

  As is apparent from the above description, in this embodiment, the portion of the controller 60 that executes S225, S227, S230, S242, S270, and S282 in FIG. It constitutes an example of a “width determining unit”.

  Next, a fifth embodiment of the present invention will be described. However, this embodiment differs from the first embodiment only in the software configuration related to command value determination, and the other software configuration and hardware configuration are common, so only the different parts will be described in detail and shared. The part which performs is quoted using the same code | symbol or name, and the duplicate description is abbreviate | omitted.

  In the first embodiment, the charging current Ic of the capacitor 14 is maximized by discretely changing the output current Is of the solar cell 12 regardless of the output voltage Vs of the solar cell 12.

  On the other hand, in the present embodiment, when the output voltage Vs of the solar cell 12 is higher than the reference value V0, current change type control that repeats discretely changing the command value Id of the output current Is is performed. On the other hand, when the output voltage Vs is not higher than the reference value V0, the voltage change type control that repeats changing the command value Id of the output voltage Is discretely is performed.

  FIG. 17 shows a charging device 300 according to the present embodiment in the same manner as FIG. The charging device 300 has the same basic configuration as the charging device 10 shown in FIG. The difference from the charging device 10 is that the charging device 300 includes an output voltage detection circuit 202 as in the charging device 200 shown in FIG.

  As shown in FIG. 17, in the charging device 300, the output terminal of the output current detection circuit 57 and the output terminal of the output voltage detection circuit 202 are connected to the two inputs of the differential amplifier 87 via the selector switch 310. It is electrically connected to one of the terminals.

  A command signal from the controller 60 is supplied to the selector switch 310 via the DA converter 82. In accordance with the command signal, selector switch 310 connects output current detection circuit 57 to differential amplifier 87, while differentiating output voltage detection circuit 202 from a current detection state in which output voltage detection circuit 202 is disconnected from differential amplifier 87. While being connected to the dynamic amplifier 87, the output current detection circuit 57 is selectively switched to a voltage detection state in which the differential amplifier 87 is cut off.

  As shown in FIG. 17, in the charging device 300, the output terminal of the output voltage detection circuit 202 is electrically connected to the controller 60 via the AD converter 56.

  FIG. 18 conceptually shows a command value determination program executed by the computer 70 of the controller 60 shown in FIG. 1 in a flowchart. The command value determination program is stored in the ROM 74.

  When the command value determination program shown in FIG. 18 is executed, first, in S1000, the output voltage Vs is detected based on the output signal of the output voltage detection circuit 202. Next, in S1010, it is determined whether or not the detected output voltage Vs is higher than the reference value V0. If it is assumed that the output voltage Vs is higher than the reference value V0 this time, the determination in S1010 is YES, and the process proceeds to S1020.

  In S1020, a command signal for realizing the current detection state is output to the selector switch 310. Thereafter, in S1030, a program common to the command value determination program shown in FIG. 7 is executed to execute one search cycle. Thereby, a current change type search is executed. Subsequently, when one search cycle by this current change type search is completed, the process returns to S1000.

  On the other hand, if it is assumed that the output voltage Vs is not higher than the reference value V0 this time, the determination in S1010 is NO, and the process proceeds to S1040.

  In S1040, a command signal for realizing the voltage detection state is output to the selector switch 310. Thereafter, in S1050, a program common to the command value determination program shown in FIG. 11 is executed to execute one search cycle. Thereby, a voltage change type search is executed. Subsequently, when one search cycle by the voltage change type search is completed, the process returns to S1000.

  As is apparent from the above description, in the present embodiment, the switch control circuit 84 and the selector switch 302 jointly constitute an example of the “duty ratio control unit” in the above section (13), and the A / D converter 56, the controller 60, and the D-A converter 82 together constitute an example of the “command value supply unit” in the same section.

  As described above, some of the embodiments of the present invention have been described in detail with reference to the drawings. However, these are exemplifications, and are based on the knowledge of those skilled in the art including the aspects described in the section of [Disclosure of the Invention]. The present invention can be implemented in other forms with various modifications and improvements.

It is an electric circuit diagram which shows the charging device according to 1st Embodiment of this invention. It is a graph showing the characteristic of the solar cell in FIG. FIG. 2 is an electric circuit diagram conceptually showing two specific examples of the filter in FIG. 1. FIG. 2 is a block diagram conceptually showing a controller in FIG. 1. It is a time chart for demonstrating each operation | movement of the triangular wave source in FIG. 1, a switch, and an electrical double layer capacitor. 3 is a time chart for illustrating a switching cycle, a sub cycle, and a search cycle in the charging device shown in FIG. 1. 5 is a flowchart conceptually showing a command value determination program shown in FIG. It is a graph for demonstrating the relationship between the output current of the solar cell in the charging device shown in FIG. 1, and the charging current of an electric double layer capacitor. It is a graph for demonstrating S240 and S280 in FIG. 7, respectively. It is an electric circuit diagram which shows the charging device according to 2nd Embodiment of this invention. FIG. 11 is a flowchart conceptually showing a command value determination program executed by a computer of the controller in FIG. 10. It is a flowchart which represents notionally the command value determination program run by the computer of the controller of the charging device according to 3rd Embodiment of this invention. 13 is a graph for explaining S221 to S224 in FIG. It is a flowchart which represents notionally the command value determination program run by the computer of the controller of the charging device according to 3rd Embodiment of this invention. It is a graph for demonstrating S227 in FIG. It is a graph which shows the time transition of step size (DELTA) I determined by execution of the command value determination program shown in FIG. It is an electric circuit diagram which shows the charging device according to 5th Embodiment of this invention. 18 is a flowchart conceptually showing a command value determination program executed by a computer of the controller in FIG.

Claims (4)

An electric double layer capacitor having a characteristic in which electric power generated by a solar cell having a maximum point with respect to the generated voltage and generated current is stored in the electric energy generated by the solar cell and the voltage changes according to the amount of the stored energy. In order to charge, it is a charging device used connected to the solar cell and the electric double layer capacitor,
A step-down switching regulator that has at least a switch and converts electric power supplied from the solar cell to the electric double layer capacitor according to a variable duty ratio of the switch;
An output current detection circuit that detects, as an actual output current, an actual value of a current output from the solar cell to the electric double layer capacitor via the switching regulator;
A duty ratio control unit that is connected to the switching regulator and the output current detection circuit, and controls the duty ratio so that the detected value of the actual output current by the output current detection circuit matches the command value of the target output current;
A capacitor current detection circuit for detecting a current of the electric double layer capacitor as a capacitor current;
The duty ratio control unit and the capacitor current detection circuit are connected to each other, and the command value of the target output current is discretely changed and supplied to the duty ratio control unit without referring to the voltage of the electric double layer capacitor. Including the command value supply section,
The command value supply unit discretely changes the command value of the target output current so that the capacitor current is substantially maximized based on the characteristics of the time change of the capacitor current with each discrete change. And
The command value supply unit repeats a subcycle for discretely changing the command value by a step size for each search cycle, so that the target output current is substantially maximized. Exploratoryly determine the optimal value of
The cycle of the sub-cycle includes E (Wh) as the stored energy of the electric double layer capacitor, P (W) as the generated power of the solar cell, and the charging voltage Vc of the electric double layer capacitor as a control error of the charging voltage Vc. When the control error rate obtained by dividing by ΔVc is expressed by γ,
(E / P) · γ
A charging device that is set so as not to exceed the value represented by using . A solar cell in which the generated power has a maximum point with respect to the generated voltage and generated current;
  An electric double layer capacitor that stores electric energy generated by the solar cell and has a characteristic that the voltage changes according to the amount of the stored energy;
  A charging device connected to the solar cell and the electric double layer capacitor to charge the electric double layer capacitor with the solar cell;
  A charging system comprising:
  The charging device is:
  A step-down switching regulator that has at least a switch and converts electric power supplied from the solar cell to the electric double layer capacitor according to a variable duty ratio of the switch;
  An output current detection circuit that detects, as an actual output current, an actual value of a current output from the solar cell to the electric double layer capacitor via the switching regulator;
  A duty ratio control unit that is connected to the switching regulator and the output current detection circuit, and that controls the duty ratio so that the detected value of the actual output current by the output current detection circuit matches the command value of the target output current;
  A capacitor current detection circuit for detecting a current of the electric double layer capacitor as a capacitor current;
  The duty ratio control unit and the capacitor current detection circuit are connected to each other, and the command value of the target output current is discretely changed and supplied to the duty ratio control unit without referring to the voltage of the electric double layer capacitor. Command value supply
  Including
  The command value supply unit discretely changes the command value of the target output current so that the capacitor current is substantially maximized based on the characteristics of the time change of the capacitor current with each discrete change. And
  The command value supply unit repeats a sub-cycle for discretely changing the command value by a step size for each search cycle, so that the target output current is substantially maximized. Exploratoryly determine the optimal value of
  The cycle of the sub-cycle includes E (Wh) as the stored energy of the electric double layer capacitor, P (W) as the generated power of the solar cell, and the charging voltage Vc of the electric double layer capacitor as a control error of the charging voltage Vc. When the control error rate obtained by dividing by ΔVc is expressed by γ,
  (E / P) · γ
A charging system that is set so that it does not exceed the value represented using. An electric double layer capacitor having a characteristic in which electric power generated by a solar cell having a maximum point with respect to the generated voltage and generated current is stored in the electric energy generated by the solar cell and the voltage changes according to the amount of the stored energy. In order to charge, it is a charging device used connected to the solar cell and the electric double layer capacitor,
A step-down switching regulator that has at least a switch and converts electric power supplied from the solar cell to the electric double layer capacitor according to a variable duty ratio of the switch;
An output voltage detection circuit for detecting an actual value of a voltage output from the solar cell to the electric double layer capacitor through the switching regulator as an actual output voltage;
A duty ratio control unit that is connected to the switching regulator and the output voltage detection circuit, and controls the duty ratio so that the detected value of the actual output voltage by the output voltage detection circuit matches the command value of the target output voltage;
A capacitor current detection circuit for detecting a current of the electric double layer capacitor as a capacitor current;
The duty ratio control unit and the capacitor current detection circuit are connected to each other and the command value of the target output voltage is discretely changed and supplied to the duty ratio control unit without referring to the voltage of the electric double layer capacitor. Including the command value supply section,
The command value supply unit discretely changes the command value of the target output voltage so that the capacitor current is substantially maximized based on the characteristics of the time change of the capacitor current accompanying the discrete change of each time. And
The command value supply unit repeats a subcycle for discretely changing the command value by a step size for each search cycle, so that the target output voltage is substantially maximized so that the capacitor current is substantially maximized. Exploratoryly determine the optimal value of
The cycle of the sub-cycle includes E (Wh) as the stored energy of the electric double layer capacitor, P (W) as the generated power of the solar cell, and the charging voltage Vc of the electric double layer capacitor as a control error of the charging voltage Vc. When the control error rate obtained by dividing by ΔVc is expressed by γ,
(E / P) · γ
A charging device that is set so as not to exceed the value represented by using . A solar cell in which the generated power has a maximum point with respect to the generated voltage and generated current;
  An electric double layer capacitor that stores electric energy generated by the solar cell and has a characteristic that the voltage changes according to the amount of the stored energy;
  A charging device connected to the solar cell and the electric double layer capacitor to charge the electric double layer capacitor with the solar cell;
  A charging system comprising:
  The charging device is:
  A step-down switching regulator that has at least a switch and converts electric power supplied from the solar cell to the electric double layer capacitor according to a variable duty ratio of the switch;
  An output voltage detection circuit for detecting, as an actual output voltage, an actual value of a voltage output from the solar cell to the electric double layer capacitor via the switching regulator;
  A duty ratio control unit that is connected to the switching regulator and the output voltage detection circuit, and controls the duty ratio so that the detected value of the actual output voltage by the output voltage detection circuit matches the command value of the target output voltage;
  A capacitor current detection circuit for detecting a current of the electric double layer capacitor as a capacitor current;
  The duty ratio control unit is connected to the capacitor current detection circuit, and the command value of the target output voltage is discretely changed and supplied to the duty ratio control unit without referring to the voltage of the electric double layer capacitor. Command value supply
  Including
  The command value supply unit discretely changes the command value of the target output voltage so that the capacitor current is substantially maximized based on the characteristics of the time change of the capacitor current accompanying the discrete change of each time. And
  The command value supply unit repeats a subcycle for discretely changing the command value by a step size for each search cycle, so that the target output voltage is substantially maximized so that the capacitor current is substantially maximized. Exploratoryly determine the optimal value of
  The cycle of the sub-cycle includes E (Wh) as the stored energy of the electric double layer capacitor, P (W) as the generated power of the solar cell, and the charging voltage Vc of the electric double layer capacitor as a control error of the charging voltage Vc. When the control error rate obtained by dividing by ΔVc is expressed by γ,
  (E / P) · γ
A charging system that is set so that it does not exceed the value represented using.

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