JP5028056B2 - Power feeding system and method for controlling power feeding system - Google Patents

Description

  The present invention relates to a power supply system including a plurality of DC power supply strings having a DC power supply and a storage battery and a power conversion device, and to supply power and a control method.

A power supply system has been developed that includes a plurality of DC power supply strings that store the power generation outputs of a plurality of DC power sources, such as solar cells or fuel cells, in each storage battery, and that outputs power as necessary.
For example, Patent Document 1 discloses a solar power generation device including a plurality of solar cell strings. In this Patent Document 1, a first solar cell string and a second solar cell string are connected in parallel, and these solar cell strings are controlled so that DC power is output at a maximum output operating point, and DC power is converted to AC. Between the power converter device which converts into electric power, and the 2nd solar cell string, the adjustment means which adjusts the output voltage of a 2nd solar cell string to the output voltage of a 1st solar cell string is provided.
Japanese Patent Laid-Open No. 2004-146791

According to Patent Document 1, it is possible to use the sum of the maximum output powers from the respective solar cell strings having different power generation capacities as the maximum output power.
By the way, when a solar cell string contains a storage battery, if the voltage of each storage battery is equal, an output can be taken out from each storage battery and the total electric power of each storage battery can be output. However, if each storage battery voltage is not equal, it is output from a storage battery with a high voltage, and an output cannot be obtained from a storage battery with a low voltage. Therefore, the total power of each storage battery cannot be obtained. Moreover, since it outputs from the storage battery with a high voltage, the use frequency of a storage battery comes to offset.
In view of the above problems, an object of the present invention is to provide a power supply system that allows the total power of each storage battery to be obtained from the power supply system and prevents a certain storage battery from being used in a biased manner. . It is another object of the present invention to provide a power feeding system that can eliminate the complicated control and can achieve the above object with a very simple circuit.

A power supply system according to the present invention includes a plurality of DC power supply strings having a DC power supply and a storage battery, a power conversion device that converts a DC output of the plurality of DC power supply strings into an AC output, and the storage battery voltages substantially equal to each other. A control unit that controls the power conversion device.
Thereby, the total electric power of each storage battery can be obtained. In addition, a certain storage battery is not used in a biased manner, and the life of the system can be extended. In addition, since the control unit controls the power conversion device to make each storage battery voltage substantially equal, it can be controlled by a very simple circuit.
In the power supply system of the present invention, it is preferable that the storage battery is charged and discharged with a predetermined current.

In addition, the power supply system of the present invention converts a plurality of DC power supply strings having a DC power supply and a storage battery, a detection unit that detects an output current of each storage battery, and a DC output of the plurality of DC power supply strings into an AC output. A power conversion device; and a control unit configured to control the storage battery voltages to be substantially equal to each other according to an output current of each storage battery detected by the detection unit.
Thus, by arranging the voltages of the storage batteries, the same amount of current can be extracted without being biased from each string, so that the power conversion device can request the maximum power from the power feeding system. . In addition, since it is only necessary to detect and control the power demand of the power conversion device or the current of the storage battery, the control targeted by the present invention can be realized by a very simple control circuit.

In the power supply system of the present invention, in the embodiment, the control unit is configured such that each of the storage battery voltages is substantially equal before the output of the power conversion device, at a predetermined time or every predetermined interval, or when the storage battery voltage reaches a predetermined voltage. It is preferable to control so that it becomes. By controlling in this way, when the power supply system outputs power, the output of each storage battery is substantially equal, so that the total power of each storage battery can be supplied.
In the power supply system of the present invention, in the embodiment, the DC power source is preferably a solar cell or a fuel cell. Thereby, the electric power generation output of a solar cell or a fuel cell can be utilized effectively. Similarly, a DC power source obtained by converting an AC power source such as a generator or a wind power generator can also be used.
In the power supply system of the present invention, in the embodiment, it is preferable that each of the DC power supply strings is connected via a backflow prevention diode. Thereby, overcharge of the storage battery provided in each DC power supply string can be prevented with a simple circuit.

According to another aspect of the present invention, there is provided a control method for a power supply system, wherein the power supply system outputs a plurality of DC power supply strings having a DC power supply and a storage battery, and a DC output of the plurality of DC power supply strings. And a second step of outputting power from the power converter. Thereby, the total electric power of each storage battery can be obtained.
Further, according to the control method of the power supply system of the present invention, when the output of the DC power supply is different, each storage battery is charged in accordance with the lowest DC power supply output amount, and the remaining DC power supply output amount is transferred to the power converter. A third step of outputting. Thereby, a power generation output can be obtained from a DC power source such as a solar cell or a fuel cell, and the amount of charge to each storage battery can be made uniform.
In the power supply system control method of the present invention, it is preferable that the output power of the power converter is gradually increased when the voltages of the storage batteries are substantially equal in the first step. When controlling in this way, a storage battery voltage can be made the same by flowing a small electric current.
In the power supply system control method of the present invention, it is preferable to check whether or not each of the storage batteries outputs the same current when the voltages of the storage batteries are substantially equal in the first step.

  According to the present invention, the total power of each storage battery can be obtained. In addition, it is possible to prevent a certain storage battery from being used in a biased manner. In addition, since the present invention does not perform complicated control, the power feeding system of the present invention can be realized by an extremely simple circuit.

(Embodiment 1)
As shown in FIG. 1, the power supply system according to Embodiment 1 of the present invention forms a DC power supply string 1 by connecting a DC power supply 1A and a storage battery 1B in parallel, and converts a plurality of such DC power supply strings in parallel. Connect to device 11. Although FIG. 1 shows a case where three DC power supply strings are connected to the power converter 11, the number of DC power supply strings is not limited and may be two or three or more.
The power converter 11 is connected to the grid linkage 20, and the power supply system of the present invention sells output power to the grid linkage 20. Alternatively, although not shown, power may be supplied to the load. A control unit 12 is connected to the power converter 11 and controls the power converter 11 as described below.
A backflow prevention diode 1C is connected to the DC power supply side from the connection point S between the DC power supply 1A and the storage battery 1B. Further, a backflow prevention diode 1D is connected between the connection point T and the connection point S of each DC power supply string. The diode 1C prevents a current flowing into the DC power supply 1A, and the diode 1D prevents power exchange between the DC power supply strings. Further, a means for ensuring the safety of the storage battery, for example, a current fuse or breaker 1E that allows current in the safe range of the storage battery is connected to the output side of the storage battery 1A.

Here, the DC power source 1A is a DC power source obtained from, for example, a solar cell or a fuel cell, but may be a DC power source obtained by converting electric power obtained from wind power generation or a generator into DC power. . In this embodiment, a solar cell will be described.
The system linkage 20 is shown as a portion that absorbs power generated by the operation of the power supply system of the present invention, and may be a storage battery as long as it can absorb output power. The power charged in the storage battery may be supplied to the load later.
The storage battery 1B provided in the DC power supply string can use many types of storage batteries such as a lead battery, a lithium ion battery, and a nickel battery. In this embodiment, the storage battery 1B will be described as a lithium ion battery. The storage battery can be replaced by an electric double layer capacitor or a superconducting power storage device.

  The power supply system of the present invention may be a small-scale solar power generation system installed in a general household, and may be a medium- or large-scale solar power installed on a roof of an apartment house, a factory, a public facility, or the like. Although it may be a power generation system, the power supply system of the present invention needs to be a plurality of DC power supply strings. Therefore, the solar cell is divided into at least two regions, and a storage battery is provided for each of the divided regions to constitute a plurality of DC power supply strings. A solar cell is configured by connecting a plurality of solar cells or a group of solar cells in series.

As a kind of solar cell in the present invention, a crystalline solar cell module produced by connecting a plurality of crystalline solar cells, a silicon-based semiconductor or a compound system formed on a glass substrate by a method such as CVD Examples include a solar cell module using cells obtained by processing semiconductor thin film solar cells so that they are connected in series, and a solar cell module using a tandem solar cell in which crystalline silicon and amorphous silicon are stacked. .
In ordinary solar power generation, the maximum power point that changes according to the sunlight conditions and the temperature of the solar cell module is tracked, and the operating point voltage is controlled so that the output power becomes maximum. However, in this invention, it operates so that the voltage of the storage battery module connected may become the operating point voltage of a solar cell module. Therefore, the operating point voltage of the solar cell module is limited to the voltage range in which the storage battery module operates.

In general, the output of a solar cell decreases as its module temperature increases, and the maximum power operating point has a linear relationship with a negative slope (temperature coefficient) with respect to temperature. Usually, the temperature coefficient of crystalline silicon is about −0.45 to −0.5% / ° C. In addition, amorphous silicon laminated with crystalline silicon and compound semiconductor solar cells such as GaAs have been developed and put into practical use with a temperature coefficient suppressed to -0.2 to -0.3% / ° C. .
On the other hand, the operating voltage of the storage battery module is not significantly affected by temperature. Therefore, it is desirable to select a solar cell having excellent temperature characteristics that is less susceptible to change in output voltage depending on temperature. As described above, it is desirable to select a solar cell module having a temperature coefficient of −0.42% / ° C. or lower, more preferably −0.3% / ° C. or lower. Thereby, high system efficiency can be obtained. Although this depends on the type of the storage battery device to be connected, the fluctuation range due to the temperature change of the operating voltage of the storage battery device is about 20 to 30%, while the operating temperature range of the solar cell module is about 60 ° C. It is calculated considering this.

In the present invention, the storage battery preferably has as much capacity as possible in a narrow voltage range, and a secondary battery using a chemical reaction is preferable. Among them, a battery system that basically does not involve a side reaction in the charge / discharge reaction is more preferable because of high power efficiency by charge / discharge. A typical example is a lithium ion battery.
Furthermore, lead-acid batteries that have been used as power storage devices until now are subject to capacity deterioration if they continue to be insufficiently charged. Although an effect etc. are seen, a lithium ion battery does not have cycle deterioration or a memory effect due to insufficient charging, and can be suitably used as a battery for constituting the power storage module of the present invention. Furthermore, since the lithium ion battery is less susceptible to changes in the charging voltage due to ambient temperature, it is very effective as a power storage system for the control method of the present invention.
Various materials for the positive electrode material and the negative electrode material have been proposed for the lithium ion battery, and all of them can be used. Among them, a lithium ion battery using LiFePO4 as the positive electrode has a flat charge / discharge curve and is particularly preferable.

  In the following description, the output current value of the storage battery needs to be suppressed to 5 A or less for the safety of the system, the rated output of each solar battery is 300 W, and the usage range of the storage battery voltage is 40 V to 60 V. These numerical values are illustrative examples and do not limit the scope of the present invention. In the following description, the current value and voltage value of each storage battery are shown for easy understanding. However, in the first embodiment, it is not necessary to detect these current values and voltage values. There is no need to prepare.

In the circuit shown in FIG. 1, the voltages of the storage batteries 1B, 2B, and 3B are all set at 40V. Thereafter, the solar cells 1A, 2A, and 3A generate solar power to charge each storage battery. However, for example, the solar cell 2A was hidden behind the clouds, and the power generation output decreased. Further, the solar cell 3A was hidden behind and did not generate electricity at all. As a result, the storage battery 1B was 50V, the storage battery 2B was 45V, and the storage battery 3B was 40V, and the voltages of the storage batteries varied. The cause of the variation in the voltage of each storage battery is caused not only by the variation in the amount of solar radiation but also by the installation direction of each solar battery, the area of each solar battery, the power generation performance of each solar battery, and the charging characteristics of each storage battery.
In this way, when the power conversion device 11 requests power in a state where the voltage of each storage battery varies, it is output from the storage battery having a high voltage. In this system, each storage battery voltage and storage battery current are not monitored. Therefore, assuming that the worst case (each storage battery voltage varies widely) is output from a single string, 5A or more is never required. Like that. Moreover, in this system, since the variation in voltage can be corrected earlier as the current is larger, 5A is preferable. In this case, since the storage battery 1B has the highest voltage, it is output from the storage battery 1B. The other storage batteries 2B and 3B cannot contribute to the output because the voltage is sufficiently lower than that of the storage battery 1B. Therefore, the power feeding system can supply power only in the allowable current range of the storage battery 1B.

  In order to eliminate the above-described variations in the storage battery voltages, the power supply system of the present invention requested the control unit 12 to output 5 A from the power converter 11. Since the storage battery 1B has a higher voltage than the other storage batteries 2B and 3B, a current flows from the storage battery 1B. At this time, assuming that the internal resistance of the storage battery 1B is 1Ω, the voltage of the storage battery 1B drops by the amount corresponding to the internal resistance and becomes substantially 45V. Therefore, it apparently becomes equal to the voltage of the storage battery 2B. Thereafter, as the discharge proceeds, the battery 2B also outputs. Of course, since the storage battery 1B has a larger discharge current for a while, the storage battery 1B is discharged more than the storage battery 2B, and the voltage decreases more quickly. Thereafter, the voltage at the connection point T is reduced to 40 V, and discharging is started from the storage battery 3B. The discharge current of the storage battery 1B at the moment when the voltage at the connection point T became 40V was 3A, and the discharge current of the storage battery 2B was 2A. The voltages of the storage battery 1B when there was no polarization due to discharge were 43V and 42V, respectively, and the voltage difference between the two storage batteries decreased from 5V to 1V at this time.

Similarly, if the power conversion device 11 continues to request 5A even after the connection point T becomes 40V, the operation is performed so that the voltages between the storage batteries are uniform, and as a result of continuing this operation, the connection point T becomes 37V. When the battery was discharged, 1.7 A was discharged from each storage battery, and the voltages were completely aligned. It has been exactly 1 hour since the controller 12 first requested the power converter to output 5A.
In this system, it is possible to arrange the storage battery voltages quickly and safely without monitoring each storage battery voltage and storage battery current by periodically making a power request from the power converter 11 with one string of withstand current. .
Here, the reason for explaining the voltage of each storage battery with the voltage at the connection point T is that the solar battery is installed on the roof or the roof, and the storage battery is installed indoors or the like. For this reason, the voltage drops by the resistance of the connection line.

As described above, the voltages of the three storage batteries can be made uniform. During this time, the power conversion device 11 only requests output power, and the control unit 12 only commands the power conversion device 11 to request output, and the voltages are naturally aligned as each storage battery outputs. No other special control is necessary. The predetermined current in this case is a current that the power conversion device requires only a current that does not flow more than an allowable current in each string. In this embodiment, the predetermined current is 5 A, but any number may be used if the current is less than 5 A. Since the power requested by the power converter 11 during this operation can be output to the grid connection and sold, the power stored in the storage battery is not wasted. Further, instead of selling power, a storage battery may be provided instead of system linkage, and the storage battery may be used to supply power as part of the power supply system of the present invention.
As described above, after selling the voltages of the three storage batteries, when the power is sold to the grid connection or when requested by the load, the control unit controls the power conversion device 11 to suppress the safety of each DC power supply string. Even if the total maximum current 15A is output by 5A from each maximum current, for example, 5A from each DC power supply string, the output can be obtained safely.

When the DC power source is a solar battery, the power supply system of this embodiment can make the voltages of the respective storage batteries uniform by operating for a certain time after a predetermined time such as sunset or evening in the day. Alternatively, control may be performed so that the voltages of the storage batteries are made uniform before the power supply system of the present invention outputs power. Alternatively, a controller is provided with a timer, and when a certain time elapses, for example, every 3 hours, the power generation output of the solar cell is different for each DC power supply string, and therefore the voltage of the storage battery is predicted to be uneven. The above operation may be performed. It is more preferable to know how often the voltage variation of the system actually occurs, because it is possible to determine how often the above control should be performed on a regular basis.
In the first embodiment, the storage battery can be charged by generating power from the solar cell, and the power generation output of the solar cell can be supplied to the system linkage or the load via the power conversion device. This will be described in 2 and 3.

(Embodiment 2)
FIG. 2 shows a power supply system according to Embodiment 2 of the present invention. The second embodiment includes current sensors 1F, 2F, and 3F that detect charging or discharging current of each storage battery, the detection output is monitored by the current detection unit 102, and the result is sent to the control unit 12, and each DC A configuration different from that of the first embodiment shown in FIG. 1 is provided with a voltage sensor 5 that detects the voltage at the connection point T of the power supply string, the detection output is monitored by the voltage detection unit 101, and the result is sent to the control unit 12. Part. Others are the same as those of the first embodiment shown in FIG. Note that FIG. 2 does not show a current fuse or breaker for ensuring the safety of the storage battery on the output side of the storage battery 1A so as not to make the drawing complicated, but it is assumed that they are connected in the same manner as in FIG. Further, the output current value of the storage battery needs to be suppressed to 10 A or less for the safety of the system.

In the circuit shown in FIG. 2, the voltages of the storage batteries 1B, 2B, and 3B are all 50V. Strictly speaking, in the second embodiment, the storage battery voltage of each DC power supply string is measured at the connection point T. For convenience, the description will be given using each storage battery voltage. Thereafter, the solar cells 1A, 2A, and 3A charged each storage battery. For example, the power generation output of the solar battery 2A and the solar battery 3A decreased. As a result, the storage battery 1B was 60V, the storage battery 2B was 55V, and the storage battery 3B was 50V. As a result, the voltage of each storage battery varied. Alternatively, variations were caused by individual differences in the performance of each solar cell and each storage battery. Since the voltage of the connection point T detects the highest storage battery voltage, 60 V is detected at this time.
Since the use area of the storage battery is 40V to 60V, when the control unit 12 detects that the voltage at the connection point T is 60V, the control unit 12 instructs the power converter 11 to request a power of 2A. Or before the said power converter device outputs, a control part commands a power request | requirement of 2A to the power converter device 11 at predetermined time or for every fixed interval.

Then, a current flows from the storage battery 1B. However, since the internal resistance of the storage battery 1B is 1Ω, a voltage drop corresponding to the internal resistance occurs to 58V substantially. Therefore, it is higher than the voltage of the storage batteries 2B and 3B, and only the storage battery 1B outputs. Then, the control part 12 increases the electric power requirement amount of the power converter device 11, and makes the voltage of the storage battery 1B become equal to the voltage of the storage battery 2B. Furthermore, the control part 12 increases the electric power requirement amount of the power converter device 11, and makes the voltage of storage battery 1B, 2B become equal to the voltage of storage battery 3B. When the voltages of the three storage batteries 1B, 2B, 3B appear to be the same, current can be output from the three storage batteries 1B, 2B, 3B.
Since the voltages of the three storage batteries can be made uniform as described above, the output power of the power converter 11 is then reduced. When the currents of the three storage batteries become the same, the control unit 12 stops the operation of the power converter, and then the power feeding system waits until there is a request for output power.

  The above description will be described in detail with reference to the flowchart shown in FIG. That is, in the power supply system, when n + 1 DC power supply strings are connected and the output of the DC power supply is different, the minimum current among the DC power supplies is Ia, and the remaining currents are I1, I2,. , (I1-Ia) + (I2-Ia) + (In-Ia) The power conversion device has a third step of controlling so as to always request the amount of power. This third step may be provided as necessary.

  When the control unit 12 detects that any of the three storage batteries 1B, 2B, and 3B has reached 60V (that is, when the voltage at the connection point T is detected to be 60V), or the three storage batteries 1B, 2B, When the output current of 3B is not equal to or greater than a predetermined value, or when a predetermined time is reached, or before the power supply system outputs power, or at a predetermined time interval, first, currents I1 and I2 flowing from the respective storage batteries , I3 is detected. The detected maximum current is set to Imax, the minimum current is set to Imin, and it is determined whether Imax is 10 A or more (S1). If Imax is 10 A or more, the required power of the power converter is reduced and the process returns to step S1. If Imax is within 10A, the process proceeds to step S3.

Next, it is determined whether Imin is output (S3). If Imin is output, the required power of the power converter is reduced (S4), and the process returns to step S3. If Imin is not output, the process proceeds to step S5.
Next, it is checked whether the currents I1, I2, and I3 are the same (S5). Here, since it is difficult to accurately satisfy I1 = I2 = I3, it is preferable to provide a range in which the difference between Imax and Imin is within 10%. If I1 = I2 = I3 (this value is almost zero), this flow is terminated. If I1 = I2 = I3 is not satisfied, the required power of the power converter is increased (S6), and the process returns to step S1.

  In the present embodiment, the power conversion device is controlled in a state where any of the three storage battery currents is discharged near zero, but when the power generation output from the solar battery is added, the detection for further detecting the combined output is performed. It is preferable to provide a section and monitor the combined output of each string and control the minimum combined output close to zero. That is, the determination criterion in step S3 is not Imin, but the minimum value of the combined output is set to a value close to zero. Thereby, it becomes possible to suppress the electric power consumption of a storage battery to the minimum, and to arrange | equalize the voltage of each storage battery at the fastest. This is because the string voltage can be said to be the same voltage as the connection point T when it is output from the string. In this way, the predetermined current means that the current that operates when Imin is not zero but near zero, or the current that operates when Imax is near the allowable current.

The voltage and current of each storage battery described above will be described below over time.
FIG. 4 is a block diagram for explaining the voltage and current of each storage battery over time, and this figure shows two DC power supply strings for the sake of simplicity. In addition, FIG. 5 shows changes in voltage and current of each storage battery with the passage of time when there is a request for power from the power converter. Here, it is assumed that each solar cell has a certain output. The storage battery with the higher initial storage battery voltage is 1B, and the storage battery with the lower storage battery voltage is 2B.
When the power converter requests power, the power is first output from the storage battery 1B having the higher storage battery voltage. If the solar battery output 1A having the higher storage battery voltage cannot cover the power required by the power conversion device, the storage battery 1B having the lower voltage is also discharged. Whether the solar battery 2A and the storage battery 2B are discharged to the power conversion apparatus or charged to the storage battery 2B is determined according to the difference between the power requirement of the power conversion apparatus and the voltage of the storage battery 1B. In FIG. 5, in the area A up to the first time T1, the power of the solar battery 2A is charged to the storage battery 2B. In FIG. 5, the storage battery 2 </ b> B is charged by the fact that the current of the storage battery 2 </ b> B is below the boundary line H between the charging and discharging of the storage battery current.

  In the region A, the above-described state continues, and when the region B from the time T1 to the time T2 is entered next, the apparent storage battery voltage is aligned. This is a state in which if the power conversion device stops requesting power in a state in which the storage battery voltages appear to be aligned due to polarization, the power conversion device will vary. In region B, the current difference between storage battery 1B and storage battery 2B is in a saturated state, and even if more power is requested from the power converter, the current difference does not increase. However, the current difference still exists, the voltage difference between the two storage batteries becomes smaller by the amount of the current difference, and finally the state in which the currents flowing through the two storage batteries are the same and the voltages are the same, after time T2 The region C shown is reached. In this region C, the voltages of the two storage batteries are really in a uniform state.

  That is, when there is a variation in each storage battery, if the state exists in the region B, it can be said that the variation of each battery is corrected at the fastest speed. As a condition that exists in the region B, it is a necessary condition that the power conversion device requires sufficient power. When the power conversion device does not require sufficient power, there is little polarization of the storage battery 1B toward the discharge side, and apparently the storage battery voltage is not uniform. In addition, when there is a large variation in voltage, if the required power of the power conversion device is increased to forcefully match the apparent storage battery voltage, the discharge current of the storage battery 1B becomes too large and the storage battery becomes overcurrent. If the wiring is burned out or the safety fuse is blown, the system cannot be secured. For the reasons described above, when the voltages of the storage batteries cannot be visually matched, it is necessary to control the power conversion device so as to request the power converter as much as possible without causing the state.

  As described above, the second embodiment can align the variations of the storage battery voltages at the fastest speed. And since the electric power requirement of a power converter device is small, each storage battery voltage can be arrange | equalized quickly, and the discharge power of a storage battery can be made small. In the description of this embodiment, the case where the power requirement of the power converter is minimized is not described, but the power requirement of the power converter is minimized by measuring and controlling the output of the solar cell. It is possible.

(Embodiment 3)
A third embodiment will be described with reference to FIG. In this third embodiment, when sensors 1F, 2F, and 3F that detect the current of the storage battery have different power generation amounts of the solar battery, a method for charging the storage battery to the maximum while preventing variations in the voltage of the storage battery in advance. Is realized. In Embodiment 3, as described in Embodiments 1 and 2, after the storage battery voltages are aligned, power is supplied by the power feeding system. And in this Embodiment 3, when the electric power generation amount of a solar cell differs, the method of charging a storage battery to the maximum is implemented as follows, preventing the dispersion | variation in the voltage of a storage battery.

FIG. 6 shows a flowchart of the third embodiment, and explains a process that can charge the battery without varying the storage battery voltage even if the power generation amount of the solar battery is different. Further, in the following description, the current values of the solar cell are shown for easy understanding, but in the third embodiment, it is not necessary to detect these current values, and therefore it is not necessary to provide a current sensor.
FIG. 7 shows the solar cell output current of each DC power supply string S1, S2, S3. The solar cell output current of string 1 is 4 A, and the solar cell output current of string 2 and string 3 is 2 A.
Now, as in the processing of the first and second embodiments, assuming that each storage battery voltage is uniform, all the solar cell outputs of each string are input to each storage battery. The battery is charged 2A more than the string storage battery. Therefore, in this state, there will be a difference in the state of charge of the storage battery.

Based on the above, description will be made with reference to the flowchart of FIG. In step S11, it is determined whether or not the voltage at the connection point T is a full charge voltage this time. If the battery is fully charged, this flowchart ends. However, if it is not the full charge voltage, X is calculated in step S12, and the value is substituted into X1. X is the difference between the maximum value and the minimum value of the output currents I1, I2, and I3 of the storage batteries 1B, 2B, and 3B. At present X1, the maximum current is 4A for the output current I1 of the solar cell 1A, the minimum current is 2A for the output currents I2 and I3 of the solar cells 2A and 3A, and the difference X1 is 2A.
Next, in step S13, X1 = X2 is determined. X2 is preferably zero as an initial value. Since X1 is currently 2A and X2 is zero, the process proceeds to step S15 to increase the required power of the power converter. If it increases by 1A, it will output from the string with many solar cell outputs, and the electric power of the area | region of the output A to B shown in FIG. 7 will be supplied to a power converter device.
In step S16, X1 is substituted for X2. As a result, the current X1 data (2A) is stored in X2.

Then, returning to the first step S11, it is determined whether or not the voltage at the connection point T is a full charge voltage. If the battery is not fully charged, the process moves to step S12, X is calculated once again, and the value is substituted into X1. The current X1 is 3A for the output current I1 of the solar cell 1A, 2A for the output currents I2 and I3 of the solar cells 2A and 3A, and the difference X1 is 1A.
Next, in step S13, X1 = X2 is determined. Since X1 is currently 1A and X2 is 2A, the process proceeds to step S15 to increase the required power of the power converter. If it is further increased by 1A, it is output from a string having a large solar cell output, and the power in the region from output A to C shown in FIG. 7 is supplied to the power converter.
In step S16, X1 is substituted for X2. As a result, the current X1 data (1A) is stored in X2.

Then, returning to the first step S11, it is determined whether or not the voltage at the connection point T is a full charge voltage. If it is not fully charged, the process moves to step S12, X is calculated once again, and the value is substituted into X1. At present X1, the maximum current is 2A for the solar cell 1A output current I1, the minimum current is 2A for the output currents I2 and I3 of the solar cells 2A and 3A, and the difference X1 is zero.
Next, in step S13, X1 = X2 is determined. Since X1 is currently zero and X2 is 1A, the process proceeds to step S15 to increase the required power of the power converter. Assuming that 1A is further increased, at present, 2A is already output from the string with the high solar cell output, so the solar cell output for each string is C point (2A), and 1 / 3A is output equally. The As a result, the power in the region of outputs A to D shown in FIG. 7 is supplied to the power conversion device.
In step S16, X1 is substituted for X2. As a result, the current X1 data (1A) is stored in X2.

Then, returning to the first step S11, it is determined whether or not the voltage at the connection point T is a full charge voltage. If the battery is not fully charged, the process moves to step S12, X is calculated once again, and the value is substituted into X1. The current X1 has a maximum current I1 = I2 = I3 = 5 / 3A, and the difference X1 is zero.
Next, in step S13, X1 = X2 is determined. Since X1 is currently zero and X2 is also zero, the process proceeds to step S14 to reduce the required power of the power converter.
In step S16, X1 is substituted for X2. As a result, the current X1 data (1A) is stored in X2. Then, it returns to step S11 and repeats this flowchart.

The above description explains the behavior in the ideal state, but in practice it is necessary to set an allowable range when determining X1 = X2 in step S13.
This system is basically controlled so that the storage battery voltage does not vary, but the voltage may actually vary slightly due to factors such as instantaneous solar radiation fluctuations. At that time, even in a region where X should be zero (lower than C in FIG. 7), it does not become zero. If the output of the power converter is maintained within the range described in the present invention, X changes in a direction approaching zero. However, the amount of change per hour in the approaching speed is small.
On the other hand, local variations in solar radiation and changes in current due to output changes of the power converter occur at relatively short time intervals. Using this difference, when the value of X changes, it is determined whether it is a change in X due to local variations in solar radiation or a change in the output of the power converter, or a change in X due to voltage variation of each storage battery. Is possible.

In the flowchart of FIG. 6, the optimum value of the allowable range is determined by setting the change amount of the required power of the power conversion device so large that the change of X due to the variation of the storage battery can be ignored in the flowchart of FIG. 6. It becomes possible.
It is preferable to set X that changes due to variations in storage batteries to be 1/5 or less, preferably 1/10 or less, more preferably 1/20, of X that changes due to output adjustment of the power converter. If it is set to 1/5 or less, step S13 may determine X1 = X2 with an error range of 20%.
With the above processing, even if the output of the solar battery varies, it is possible to make the charging power to each storage battery uniform, and it is possible to charge the battery as much as possible while suppressing the voltage variation of each storage battery. Generally speaking, for example, when n + 1 DC power supply strings are connected, let the minimum current among the DC power supplies be Ia, and the remaining DC power supply currents be I1, I2,. , (I1-Ia) + (I2-Ia) + (In-Ia) When the power converter always requests an amount of electric power greater than or equal to (In-Ia), the current values of the respective storage batteries can all be unified to Ia. It is possible to charge as much as possible while suppressing the voltage variation.

1 shows a block diagram of Embodiment 1. FIG. The block diagram of the experiment form 2 is shown. 6 shows a flowchart of Embodiment 2. The block diagram for demonstrating the time passage of each storage battery voltage and electric current is shown. The time course of each storage battery voltage and current is shown. 10 shows a flowchart of Embodiment 3. The figure explaining the process of Embodiment 3 is shown.

Explanation of symbols

1A, 2A, 3A Solar cells 1B, 2B, 3B Storage batteries 1C, 2C, 3C Diodes 1D, 2D, 3D Diodes 1E, 2E, 3E Current sensor 11 Power converter 12 Controller

Claims (8)

A plurality of DC power supply strings having a DC power supply and a storage battery;
A power converter that converts the DC output of the plurality of DC power supply strings into an AC output;
And a control unit that controls the power converter so that the storage battery voltages are substantially equal.   The power storage system according to claim 1, wherein the storage battery is charged and discharged with a predetermined current. A plurality of DC power supply strings having a DC power supply and a storage battery;
A detection unit for detecting an output current of each storage battery;
A power converter that converts the DC output of the plurality of DC power supply strings into an AC output;
A control unit that controls each storage battery voltage to be substantially equal by an output current of each storage battery detected by the detection unit;
A power supply system comprising:   The control unit controls the storage battery voltages to be substantially equal before the power conversion device outputs power, at a predetermined time or at regular intervals, or when the storage battery voltage reaches a predetermined voltage. The power feeding system according to any one of claims 1 to 3.   5. The power feeding system according to claim 1, wherein each of the DC power supply strings is connected via a backflow prevention diode. The power supply system includes a plurality of DC power supply strings having a DC power supply and a storage battery, and a power conversion device that converts a DC output of the plurality of DC power supply strings into an AC output,
A first step of controlling the voltages of the storage batteries to be substantially equal;
And a second step of outputting power from the power converter.   In the method of controlling the power supply system, when n + 1 DC power supply strings are connected and the output of the DC power supply is different, the minimum current among the DC power supplies is Ia, and the remaining currents are I1, I2,. -If it is set to In, it has the 3rd process controlled so that a power converter may always request | require the electric energy more than (I1-Ia) + (I2-Ia) + ... (In-Ia). A method for controlling the power feeding system according to claim 6.   7. The method of controlling a power feeding system according to claim 6, wherein in the first step, when the voltages of the storage batteries are made substantially equal, it is checked whether or not the storage batteries are all outputting the same current. .

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