JPH09258838A - Maximum electric power control method for photovolatic power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reach a maximum power point in a short time, to eliminate the deviation from the maximum power point, and to eliminate the stop of an inverter in the case of abrupt variation in the quantity of solar radiation by reducing the variation width of a target solar battery operating voltage each time the direction of varying the target solar battery operating voltage is inverted. SOLUTION: When current solar battery output power is larger than last solar battery output power in case of variation in solar battery operating voltage with the target solar battery operating voltage in every specific time, the direction of the variation of the target solar battery operating voltage is set to the same direction and when smaller, the direction of the variation is inverted; and the variation width of the target solar battery operating voltage is made small each time the direction of the variation in inverted. Further, the variation width of the target solar battery operating voltage is made large if the current solar battery output power varies by more than a specific value from the last solar battery output power when the solar battery operating voltage varies as the target solar battery operating voltage in every specific time varies.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for constantly extracting maximum electric power from a solar cell in a solar power generation system.

[0002]

2. Description of the Related Art FIG. 10 shows, for example, JP-A-61-197721.
It is a block diagram of the conventional solar power generation system shown by the publication. 11 is a time chart showing the operation of the conventional solar power generation system, FIG. 12 is a diagram showing the output power-output voltage characteristics of the solar cell when the amount of solar radiation is large and small, and FIG. 13 is the amount of solar radiation being large and medium. -The figure which shows the output power-output voltage characteristic of a solar cell in the case of a small case, and FIG. 14 is a figure which shows the output power-output voltage characteristic of a solar cell when the temperature of a solar cell is high / low.

In the figure, 1 is a solar cell, 2 is a voltage type inverter (hereinafter referred to as an inverter), 3 is a coupling reactor, 4 is an AC power source, 5 is a voltage detector, 6 is a voltage reference device, and 7 is an adder. , 8 is an inverter control circuit, and 9 is a current detector.

Next, a maximum power control method for the solar power generation system will be described with reference to FIG. First, a description will be given based on the characteristics of the amount of solar radiation. In the initial tracking of the maximum power point, the initial value of the solar cell operating voltage is set to the no-load voltage V in the figure.
Set it to 1. After that, the operating voltage of the solar cell is decreased in a certain width in a predetermined sampling period. During this period, the solar cell output power shifts and increases in the direction shown in the figure.

However, if the operating voltage of the solar cell is lowered as it is, the output power of the solar cell will eventually exceed the maximum power point M2 and will move in the direction of and decrease. Therefore, it is detected that the output power of the solar cell has shifted to the direction, and the operating voltage of the solar cell is changed to increase in a certain width. When the solar cell operating voltage is controlled to increase, the solar cell output power shifts to and increases again, but when the maximum power point M2 is exceeded, it shifts to and starts decreasing. . Then, the shift to the direction of is detected and the operating voltage of the solar cell is changed to the direction of decreasing again.

As described above, when the solar cell operating voltage is varied and the solar cell output power is increased, the solar cell operating voltage is continuously changed in the same direction, and when the solar cell output power is decreased, the solar cell operation is performed. Reverses the direction of voltage change. By repeating the above operation, the maximum power point M2 is searched, the solar cell operating point reciprocates near the maximum power point M2, and the solar cell is operated near the maximum power point M2.

Further, when operating near the maximum power point M2 in the characteristic of the amount of solar radiation, if the amount of solar radiation increases and the characteristic shifts to a large amount of solar radiation, the operating point of the solar cell shifts to B.
Since the solar cell operating voltage is constantly increased / decreased within a certain range, the same operation as the search for the maximum power point M2 in the characteristics during the amount of solar radiation is performed, and the solar cell operating point is in the vicinity of the maximum power point M1. It reciprocates and is operated near the maximum power point M1. Conventionally, a maximum power control method for performing the above operation has been proposed.

[0008]

In the conventional maximum power control method for a solar power generation system as described above, for example, as shown in FIG.
As shown by the solid line (a) in 1, when the constant change width (D1) for increasing / decreasing the solar cell operating voltage is large, the maximum power point is reached in a short time (T1), The deviation (D2) from the maximum power point becomes large, and the maximum power cannot be extracted from the solar cell,
There was a problem that efficiency became poor.

In particular, for example, when the solar cell operating voltage is fluctuated with the same constant change width as the large solar radiation amount characteristic as shown in FIG. 12, the operating point is G-
Since it makes a round trip between H, the deviation from the maximum power point M3 appears more conspicuously, the maximum power cannot be taken out, and the efficiency becomes poor.

Further, for example, as shown by the dotted line (b) in FIG. 11, when the constant change width (D3) for increasing / decreasing the solar cell operating voltage is small, the deviation from the maximum power point (D)
Although 4) becomes small, there is a problem that it takes time (T2) to reach the vicinity of the maximum power point and cannot follow a rapid change in the amount of solar radiation.

In particular, for example, when the amount of solar radiation is suddenly reduced and suddenly becomes small during operation near the maximum power point M1 in the characteristic of large amount of solar radiation shown in FIG. 13, the operating point becomes a point. It becomes point C from M1. As a result, there has been a problem that the output power of the solar cell becomes zero and the inverter 2 stops.

Further, in FIG. 10, a commercial system power source is usually connected to the AC power source 4 for parallel operation. Here, the commercial system voltage fluctuates by several% around the rated voltage, and even if the commercial system voltage fluctuates by several% on the high side, the inverter 2 can be operated in parallel with the commercial system power supply.
In order to secure the input voltage of, the lower limit value is set for the solar cell operating voltage.

However, as shown in FIG. 14, for example, when the solar cell temperature changes from low to high even with the same amount of solar radiation, the maximum power point shifts from point M1A to point M1B, Battery operating voltage is V2 to V3
To lower voltage. As a result, the maximum power point M
The operating voltage V3 of 1B becomes lower than the lower limit value V4 of the operating voltage of the solar cell, which causes a problem that the maximum electric power cannot be taken out from the solar cell.

The present invention has been made to solve the above problems, and can reach the maximum power point in a short time, eliminate the deviation from the maximum power point, and respond to sudden changes in solar radiation by an inverter. An object of the present invention is to provide a maximum power control method for a photovoltaic power generation system that can eliminate the stoppage of a (power converter) and can extract more power from the solar cell even when the temperature of the solar cell is high.

[0015]

A maximum power control method for a photovoltaic power generation system according to the present invention is a power converter for converting DC power generated by a solar cell into AC power and outputting the AC power. It has a control unit that calculates the output voltage of the solar cell by detecting the output voltage and output current of the battery, calculates the target solar cell operating voltage of the solar cell by the control unit every predetermined time, and the solar cell by the power converter. It is a maximum power control method of a solar power generation system that controls the solar cell output power so that the operating voltage matches the target solar cell operating voltage, and changes to the maximum power. Therefore, when the solar cell operating voltage changes, if the current solar cell output power is larger than the previous solar cell output power, change the target solar cell operating voltage direction. Flip set direction, reversing the direction of change is smaller, and is intended to reduce the change width of the target solar cell operation voltage each time reversing.

In addition, when the solar cell operating voltage changes with the change of the target solar cell operating voltage at every predetermined time, if the current solar cell output power changes by a predetermined value or more than the previous solar cell output power. Is to increase the variation range of the target solar cell operating voltage.

Furthermore, when the operating voltage of the solar cell changes with the change of the target operating voltage of the solar cell at every predetermined time, the operating voltage of this time is larger or smaller than the operating voltage of the previous time. If the above occurs for a predetermined number of times in succession, the change width of the target solar cell operating voltage for each predetermined time is increased.

Further, the maximum variation range of the target solar cell operating voltage is determined according to the present value of the output current of the solar cell, the output power of the solar cell, the output current of the power converter, or the output power of the power converter. A value is set, and when the target solar cell operating voltage changes every predetermined time, the change width of the target solar cell operating voltage is not made larger than the maximum value.

Further, the maximum value of the variation width of the target solar cell operating voltage is the present value of any one of the output current of the solar cell, the output power of the solar cell, the output current of the power converter and the output power of the power converter. It is proportional.

Further, when the solar cell operating voltage changes with the change of the target solar cell operating voltage at every predetermined time, the current solar cell output power decreases by a predetermined value or more as compared with the previous solar cell output power. In this case, the target solar cell operating voltage is lowered regardless of the case where the target solar cell operating voltage is reversed in this direction.

In addition, when the solar cell operating voltage changes with the change of the target solar cell operating voltage at every predetermined time, the current solar cell output power increases by a predetermined value or more as compared with the previous solar cell output power. In this case, the target solar cell operating voltage is raised regardless of the case where the target solar cell operating voltage is reversed in this direction.

Further, the commercial power system connected to the output of the power converter is provided, the system voltage and the system frequency of the commercial power system are detected by the control unit, and AC power synchronized with the system voltage and the system frequency is generated. As described above, the power converter is controlled as described above, the lower limit value of the solar cell operating voltage is set in proportion to the system voltage, and the target solar cell operating voltage is not made lower than the lower limit value of the solar cell operating voltage.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1. First Embodiment FIG. 1 is a block diagram of a solar power generation system showing a first embodiment of the present invention. 2, 3,
FIG. 4 is a flow chart showing the operation of the control circuit 3 (described later), and FIGS. 2 and 3 are flow charts showing a series of operations, but are shown in two separate sections for convenience. The operation of FIGS. 2 and 3 is repeatedly executed at an interval t0 of about several seconds, and the operation of FIG. 4 is repeatedly executed at an interval t1 of about several msec.

FIG. 5 is a diagram showing a solar cell output current I _S -output voltage V _S characteristic in the case of a certain amount of solar radiation, FIG. 6 is a time chart showing the operation of the solar power generation system, and FIG. 7 is a solar cell output current I FIG. 8 is a diagram showing the relationship between _S and the maximum change range V _KMAX of the solar cell operating voltage, FIG. 8 is a time chart showing the operation of the photovoltaic power generation system, and FIG. 9 is a system voltage V _AC of the commercial power system and the solar cell operating voltage lower limit value V. It is a figure which shows the relationship with _DMIN .

In the figure, 1 is a solar cell that generates direct current power from sunlight, and 2 is a power converter that converts the direct current power of the solar cell 1 into alternating current power, which is connected to a commercial power system 4 and operated in parallel. Is done. Reference numeral 10 controls the power converter 2 so that the output of the power converter 2 is synchronized with the grid voltage and grid frequency of the commercial power grid 4, and detects the output voltage and output current of the solar cell 1 to output the output power. A control circuit that calculates and controls the output current of the power converter 2 so that the output voltage of the solar cell 1 becomes a predetermined value, and shows a control unit.

The same or corresponding parts as those of the conventional example are designated by the same reference numerals. Next, the maximum power control method of the solar power generation system by the control circuit 10 will be described. Before the description with FIGS. 2 and 3, the description with FIG. 4 will be given. The flowchart of FIG. 4 controls the solar cell output voltage V _S so as to match the target solar cell operating voltage V _DN calculated by FIGS. 2 and 3.

First, the solar cell output voltage V _S is read in S300, and compared with the target solar cell operating voltage V _DN calculated in FIGS. 2 and 3 in S301. If the solar cell output voltage V _S is higher than the target solar cell operating voltage V _DN , the AC output current I _OUT of the power converter 2 is increased by a predetermined value α in S303. This also increases the solar cell output current I _S, the solar cell output current I _S in Figure 5 - the output voltage V _S characteristic,
The output voltage V _S will drop.

If the solar cell output voltage V _S is smaller than the target solar cell operating voltage V _DN in S301, the AC output current I _OUT of the power converter 2 is reduced by a predetermined value α in S302. This also reduces the solar cell output current I _S, the solar cell output current I _S in Figure 5 - the output voltage V _S characteristic,
The output voltage V _S will rise.

The above operation of S300 to S303 is t1.
By repeating at high speed every (several msec), the solar cell output voltage V _S is controlled so as to match the target solar cell operating voltage V _DN . In FIG. 1, the AC output current I
The voltage and the AC output current of the commercial power system 4 are detected and the power converter 2 is feedback-controlled so that _OUT has a value synchronized with the commercial power system 4, but the detailed description is omitted.

Next, description will be made with reference to FIGS. FIG.
The flowchart of FIG. 3 calculates the target solar cell operating voltage V _DN . First, in S200, the solar cell output voltage V _S is read. Next, in S201, the solar cell output voltage V _S is compared with the operable input voltage V1 of the power converter 2. When it is determined that the amount of solar radiation is small and the solar cell output voltage V _S is lower than the operable input voltage V1, it is determined that the power converter 2 cannot be operated, and the operation of the power converter 2 is stopped in S202. .

At the same time, the variation width V _K of the solar cell operating voltage is initialized to β in S203, the target solar cell operating voltage V _DN is initialized to (V1-β) in S204, and further, S2
F represents the change direction of the target solar cell operating voltage V _DN at 05
"-1" is set to 1 and F2, the current solar cell output power P _{NOW is set} to zero, and the process ends.

On the other hand, when the amount of solar radiation is large and it is determined in S201 that the solar cell output voltage V _S is higher than the operable input voltage V1, it is determined that the power converter 2 is operable, and in S206. The operation of the power converter 2 is started. Thus, the power converter 2, the solar cell output voltage V _S to control the AC output current synchronized with the system voltage and a system frequency of the commercial power system 4 so that the target solar cell operating voltage V _DN.

Then, in S207, the solar cell output power P
Substituting PV output power P _NOW calculated last time into _OLD , S
At 208, the solar cell output current I _S is read. And S
In 209, the solar cell output power P _NOW (= solar cell output voltage V _S × solar cell output current I _S ) is newly calculated. Through the series of operations from S207 to S209, the solar cell output power calculated last time is set as P _OLD , and the solar cell output power calculated this time is set as P _NOW .

Next, the operation of S210 to S217 will be described. First, F1 indicates the direction in which the previous solar cell operating voltage has been changed, and F2 indicates the direction in which the previous solar cell operating voltage has been changed. That is, "1" (positive) is set to F1 when the solar cell operating voltage has been increased last time, and "-1" (negative) is set to F1 when it has decreased. Similarly, "1" (positive) is set to F2 if the solar cell operating voltage has risen the previous time, and "-1" if it has fallen.
(Negative) is set.

If both F1 and F2 are negative in S210 and S211, that is, if the solar cell operating voltage has dropped both in the previous time and in the previous time, the change width V _K of the solar cell operating voltage is increased by 1.5 times in S212. . In S210 and S211, F1 is negative and F2 is positive, that is, the solar cell operating voltage was decreased last time, but if the solar cell operating voltage was increased last time,
In step S212, the change width of the solar cell operating voltage is multiplied by 0.7.

If F1 and F2 are both positive in S210 and S214, that is, if the solar cell operating voltage has increased both in the previous time and in the previous time, the change width V of the solar cell operating voltage in S215.
_{Increase K} by 1.5 times. F1 is positive in S210 and S214,
If F2 is negative, that is, the solar cell operating voltage was increased last time, but the solar cell operating voltage was decreased the previous time, S2
At 16, the variation width V _K of the solar cell operating voltage is multiplied by 0.7.

By the above operation, if the solar cell operating voltage is changed in the same direction in the previous time and the previous time, the change width V _K of the solar cell operating voltage becomes 1.5 times, and If the change direction of the battery operating voltage is different, the change width V _K of the solar cell operating voltage becomes 0.7 times. That is, if the solar cell operating voltage changes continuously in the same direction, the solar cell operating voltage change width V _K increases by 1.5 times, as shown in FIG.
Of (r) as part, variation V _K of the solar cell operating voltage
Becomes larger.

If the change direction of the solar cell operating voltage is reversed every time, the change width V _K of the solar cell operating voltage is decreased by 0.7 times, and the solar cell operation is reduced as shown in part (s) of FIG. The change width V _{K of the} voltage becomes smaller and approaches the maximum power solar cell operating voltage M2. Furthermore, S21
In step 7, processing for setting the direction F1 in which the previous solar cell operating voltage was changed to the direction F2 in which the previous previous solar cell operating voltage was changed is performed for the next control.

Next, the operation of S218 to S220 will be described. In step S218, the maximum variation range V _KMAX of the solar cell operating voltage according to the value of the solar cell output current I _S is searched and determined using FIG. Here, the relationship between the solar cell output current I _S and the solar cell operating voltage maximum change width V _KMAX is set to be proportional. Next, in S219, the variation width V _K of the solar cell operating voltage is
And the solar cell operating voltage maximum change width V _KMAX are compared.

If the variation range V _K of the solar cell operating voltage is larger than the maximum variation range V _{KMAX of the} solar cell operating voltage, S220
The solar cell operating voltage maximum variation range V _KMAX is set to the solar cell operating voltage variation range V _K. That is, the variation range V _K of the solar cell operating voltage is limited so as not to be larger than the maximum variation range V _KMAX of the solar cell operating voltage.

Next, the operation of S221 to S223 will be described. In step S221, the deviation ΔP between the previous solar cell output power P _OLD and the current solar cell output power P _NOW is calculated.
In S222, the absolute value of the deviation ΔP is compared with the predetermined value λ. Therefore, if the absolute value of the deviation ΔP has changed by the predetermined value λ or more, the maximum variation range V _KMAX of the solar cell operating voltage is set to the variation range V _K of the solar cell operating voltage in S223.

That is, the solar cell output power P _NOW
Changes from the previous solar cell output power P _OLD by a predetermined value λ or more, the variation range V _K of the solar cell operating voltage becomes the maximum variation range V _KMAX of the solar cell operating voltage. That is, as shown in part (n) of FIG. 6, the amount of solar radiation suddenly changes during operation at the maximum power solar cell operating voltage M2 at the maximum power point, the output power of the solar cell suddenly changes, and the maximum power solar cell operating voltage When M1 is reached, the maximum variation range V _KMAX of the solar cell operating voltage is set to the variation range V _K of the solar cell operating voltage.

If the output power of the solar cell has decreased by -γ or more in S224, the operations of S232 to S234 are performed. S
The operation of steps 232 to S234 will be described later in detail, but this operation is an operation of decreasing the solar cell operating voltage. That is, when the solar cell output power decreases by -γ or more, the solar cell operating voltage drops.

That is, when the solar cell output power decreases by -γ or more, it is determined that the amount of solar radiation has decreased sharply.
As can be seen from FIG. 3, the operating voltage of the solar cell that becomes the maximum power is low, so as shown in (P) part of FIG.
Even when the change direction of the current solar cell operating voltage is reversed to the rising direction, the solar cell operating voltage is decreased by the operations of steps S224, S232 to S234.

When the solar cell output power increases by ζ or more in S225, the operations of S235 to S237 are performed. S23
The operation of 5 to S237 will be described in detail later, but this operation is a process of increasing the solar cell operating voltage. That is, when the solar cell output power increases by ζ or more,
The solar cell operating voltage rises.

That is, when the output power of the solar cell increases by ζ or more, it is determined that the amount of solar radiation has rapidly increased.
As can be seen from Fig. 3, the operating voltage of the solar cell that becomes the maximum power is high, so even if the (W) part of FIG.
Even when the change direction of the present solar cell operating voltage is reversed to the lowering direction, the operating voltage of the solar cell is increased by the operations of steps S225, S235 to S237.

Next, in the operations of S226 to S228, when the operating voltage of the solar cell is changed last time, it is determined in which direction the solar cell output power characteristic moves, as shown in FIG. . First, it is determined in S226 that the current solar cell operating voltage V _DN is higher than the previous solar cell operating voltage V _DO , and in S228 the current solar cell output power P _NOW is greater than the previous solar cell output power P _OLD. For example, it can be determined that the movement is in the direction of.

Similarly, in S226, the current solar cell operating voltage V _DN is smaller than the previous solar cell operating voltage V _DO ,
If the current solar cell output power P _NOW is smaller than the previous solar cell output power P _OLD in S227, it can be determined that the solar cell is moving in the direction of, and the current solar cell operating voltage V _DN is the previous one in S226. It is larger than the solar cell operating voltage V _DO , and the current solar cell output power P _{NOW at} S228.
Is smaller than the previous solar cell output power P _OLD , the current solar cell operating voltage V _DN is smaller than the previous solar cell operating voltage V _DO in S226, and the current solar cell output power P _NOW is S227. Previous solar cell output power P
If it is larger than _OLD , it can be determined that it is moving in the direction of.

Next, the operation when moving in the respective directions from to will be described. When it is determined that the movement has been made in the directions of S226 to S228, the operations of S229 to S231 are performed. Set the current of the solar cell operating voltage V _DN to the last of the solar cell operating voltage V _DO in S229, the current of the solar cell operating voltage V _DN in S230 "of the current solar cell operating voltage V
_DN + solar cell operating voltage change width V _K "is set. By the operations of S229 and S230, the present solar cell operating voltage V _DN becomes the previous solar cell operating voltage V _DO , and the new solar cell operating voltage V _DN is the variation width V _{K of the} solar cell operating voltage.
It will be an increased value. Further, since the solar cell operating voltage is changed to the rising direction in S230, the direction F1 in which the previous solar cell operating voltage is changed is "1" in S231.
Set (positive).

If it is determined that the movement is in the directions of S226 to S228, the operations of S232 to S234 are performed. In step S232, the current solar cell operating voltage V _DN is set to the previous solar cell operating voltage V _DO , and in step S233, the new current solar cell operating voltage V _DN is set to a value decreased by the variation range V _K of the solar cell operating voltage. Become. Further, since the solar cell operating voltage is changed to the decreasing direction in S233, the direction F1 in which the previous solar cell operating voltage is changed in S234 is set to "-1".
(Negative) ”is set.

Further, when it is determined that the movement has been made in the directions of S226 to S228, the operations of S235 to S237 are performed. In S235, the current solar cell operating voltage V _DN is set to the previous solar cell operating voltage V _DO , and in S236, the new current solar cell operating voltage V _DN is a value increased by the variation range V _K of the solar cell operating voltage. Become. Furthermore, since the solar cell operating voltage is changed in the rising direction in S236, S237
Then, in the direction F1 in which the previous solar cell operating voltage was changed, "1"
(Correct) ”is set.

If it is determined that the movement is in the directions of S226 to S228, the processing of S238 to S240 is performed. In S238, the current solar cell operating voltage V _DN is set to the previous solar cell operating voltage V _DO , and in S239, the new current solar cell operating voltage V _DN is set to a value decreased by the variation range V _K of the solar cell operating voltage. Become. Further, since the solar cell operating voltage is changed to the decreasing direction in S239, the direction F1 in which the previous solar cell operating voltage is changed in S240 is "-".
Set to 1 ”(negative).

Next, in the operations of _S241 to _S243 , the lower limit value V _DMIN of the solar cell operating voltage is determined according to the system voltage V _AC of the commercial power system 4, and the solar cell operating voltage is set to the lower limit value V _D.
Control so that it does not _fall below _DMIN . First, as shown in FIG. 9, the relationship between the system voltage V _AC and the solar cell operating voltage lower limit value V _DMIN is proportional. Therefore, in S241, the solar cell operating voltage lower limit value V _DMIN is determined according to the system voltage V _AC . Next, in S242, the current solar cell operating voltage V _DN and the solar cell operating voltage lower limit value V _DMIN are compared. If the solar cell operating voltage V _DN is small, the solar cell operating voltage V _DN is calculated in S243.
_DN is limited by the solar cell operating voltage lower limit value V _DMIN .

As a result, as shown in FIG. 14, the solar cell temperature changes from a low state to a high state, and the maximum power point is point M.
Even when shifting from 1A to M1B, by limiting the solar cell operating voltage V _DN by the solar cell operating voltage lower limit value V _DMIN , when the system voltage V _AC is low, the maximum power point M1B
, And more power can be drawn from the solar cells.

[0055] In accordance with this embodiment 1, the solar cell operating voltage to set the maximum change width V _KMAX, the solar cell operating voltage up to the solar cell output current I _S in response to the current value of the solar cell output current I _S Although the control method for making the relationship with the change width V _KMAX to be a proportional relationship has been shown, any one of the current output power of the solar cell, the output current of the power converter, or the output power of the power converter is shown. The solar battery operating voltage maximum change width V _KMAX is set according to the value, and any one of the current output power of the solar cell, the output current of the power converter, or the output power of the power converter and the solar cell is set. Control may be performed so that the relationship with the maximum change range V _KMAX of the operating voltage is proportional.

In the first embodiment, at the start of control,
Although the description has been focused on starting from the direction of decreasing the solar cell operating voltage, the same effect can be obtained by starting from the direction of increasing the solar cell operating voltage.

[0057]

As described above, according to the present invention, the change width of the solar cell operating voltage is controlled to be small each time the solar cell output power is reversed from increasing to decreasing and vice versa. The effect that the operating voltage of the solar cell can be brought close to the maximum power point in a short time, and finally the deviation from the maximum power point is small, and the operating points are almost the same, and the maximum power can be extracted from the solar cell. There is.

In addition, when the solar cell operating voltage changes with the change of the target solar cell operating voltage for each predetermined time, if the current solar cell output power changes by a predetermined value or more than the previous solar cell output power. Changes the target solar cell operating voltage, so if the amount of solar radiation suddenly changes during operation at the maximum power point and the output power of the solar cell suddenly changes, the target solar cell operating voltage changes significantly. Therefore, the solar cell operating voltage can be moved to a new maximum power point quickly.

Further, when the operating voltage of the solar cell changes with the change of the target operating voltage of the solar cell at every predetermined time, the operating voltage of this time is larger or smaller than the operating voltage of the previous time. If the above occurs continuously for a predetermined number of times, the change range of the target solar cell operating voltage for each predetermined time is increased, so when the solar cell operating voltage is far from the maximum power point due to a sudden change in the amount of solar radiation. However, there is an effect that the operating voltage of the solar cell can be quickly moved to a new maximum power point.

Further, the maximum change width of the target solar cell operating voltage is determined according to the present value of the output current of the solar cell, the output power of the solar cell, the output current of the power converter, or the output power of the power converter. Set the value and when the target solar cell operating voltage changes every predetermined time, the range of change of the target solar cell operating voltage is not made larger than the maximum value. This has the effect of preventing the width from unnecessarily increasing.

Further, the maximum value of the change width of the target solar cell operating voltage is the present value of the output current of the solar cell, the output power of the solar cell, the output current of the power converter, or the output power of the power converter. Since it is proportional, the range of change is large when the amount of solar radiation is large, and the range of change is small when the amount of solar radiation is small, and the solar cell operating voltage swings largely near the maximum power point especially when the amount of solar radiation is small. There is an effect that can prevent.

Further, when the solar cell operating voltage changes with the change of the target solar cell operating voltage for each predetermined time, the current solar cell output power decreases by a predetermined value or more as compared with the previous solar cell output power. In this case, the target solar cell operating voltage is lowered regardless of the case where the target solar cell operating voltage is reversed to increase in this time.Therefore, when the target solar cell operating voltage is reduced by a predetermined value or more, it is determined that the amount of solar radiation has decreased sharply. In this case, the solar cell operating voltage, which is the maximum power, becomes low.Therefore, even when the direction of change in the solar cell operating voltage this time is reversed, the solar cell operating voltage is lowered and a new maximum power point is set. The effect is that detection can be performed quickly and the power converter will not stop.

In addition, when the solar cell operating voltage changes with the change of the target solar cell operating voltage at every predetermined time, the current solar cell output power increases by a predetermined value or more as compared with the previous solar cell output power. In this case, the target solar cell operating voltage is increased regardless of the case where the target solar cell operating voltage is reversed in this direction.Therefore, if the target solar cell operating voltage is increased by a predetermined value or more, it is determined that the amount of solar radiation has increased rapidly. In this case, the solar cell operating voltage, which is the maximum power, becomes high, so even if the change direction of the solar cell operating voltage this time is reversed, the solar cell operating voltage is increased and a new maximum power point is set. The effect is that it can be detected quickly.

Further, the control unit detects the system voltage and the system frequency of the commercial power system, controls the power converter so as to generate the AC power synchronized with the system voltage and the system frequency, and is proportional to the system voltage. Set the lower limit value of the solar cell operating voltage, and the target solar cell operating voltage is not lower than the lower limit value of the solar cell operating voltage, so when the system voltage is low,
There is an effect that the lower limit of the operating voltage of the solar cell can be brought closer to the maximum power point and more power can be taken out from the solar cell.

[Brief description of drawings]

FIG. 1 is a block diagram of a solar power generation system according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing an operation of a control circuit of the solar power generation system according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing an operation of a control circuit of the photovoltaic power generation system according to Embodiment 1 of the present invention.

FIG. 4 is a flowchart showing an operation of the control circuit of the solar power generation system according to the first embodiment of the present invention.

FIG. 5 is a diagram showing an output current-output voltage characteristic of a solar cell.

FIG. 6 is a time chart showing the operation of the solar power generation system according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between a solar cell output current and a solar cell operating voltage maximum change width of the solar power generation system according to the first embodiment of the present invention.

FIG. 8 is a time chart showing an operation of the solar power generation system according to the first embodiment of the present invention.

FIG. 9 is a diagram showing a relationship between a system voltage of a commercial power system of the solar power generation system according to the first embodiment of the present invention and a solar cell operating voltage lower limit value.

FIG. 10 is a configuration diagram of a conventional photovoltaic power generation system.

FIG. 11 is a time chart showing the operation of the conventional photovoltaic power generation system.

FIG. 12 is a diagram showing output power-output voltage characteristics of a solar cell when the amount of solar radiation is large / small.

FIG. 13 is a diagram showing output power-output voltage characteristics of a solar cell when the amount of solar radiation is large, medium, and small.

FIG. 14 is a diagram showing output power-output voltage characteristics of a solar cell when the temperature of the solar cell is high / low.

[Explanation of symbols]

1 solar cell, 2 power converter, 4 commercial power system, 10 control circuit

Claims (8)

[Claims] 1. A power converter that converts direct-current power generated by a solar cell into alternating-current power and outputs it as solar cell power, and calculates output power of the solar cell by detecting output voltage and output current of the solar cell. The control unit calculates a target solar cell operating voltage of the solar cell by the control unit every predetermined time, and the solar cell output power so that the solar cell operating voltage matches the target solar cell operating voltage by the power converter. Is a maximum power control method of the solar power generation system to control the maximum power, with the change of the target solar cell operating voltage every predetermined time,
When the solar cell operating voltage changes, if the current solar cell output power is larger than the previous solar cell output power, set the changing direction of the target solar cell operating voltage to the same direction, and if it is smaller, Is inverting the changing direction, and reducing the change width of the target solar cell operating voltage each time the inverting is performed, the maximum power control method of the solar power generation system. 2. When the solar cell operating voltage changes with the change of the target solar cell operating voltage at every predetermined time, the current solar cell output power changes by a predetermined value or more from the previous solar cell output power. The maximum power control method of the photovoltaic power generation system according to claim 1, wherein the change width of the target solar cell operating voltage is increased. 3. The solar cell operating voltage of this time is larger or smaller than the previous solar cell operating voltage when the solar cell operating voltage changes with the change of the target solar cell operating voltage every predetermined time. The maximum power of the solar power generation system according to claim 1 or 2, wherein the change width of the target solar cell operating voltage for each predetermined time is increased when a predetermined number of consecutive occurrences occur. Control method. 4. The change of the target solar cell operating voltage according to the present value of the output current of the solar cell, the output power of the solar cell, the output current of the power converter, or the output power of the power converter. The maximum value of the width is set, and when the target solar cell operating voltage changes at every predetermined time, the change width of the target solar cell operating voltage is not made larger than the maximum value of the change width. Item 3. A maximum power control method for a solar power generation system according to Item 3. 5. The maximum value of the change width of the target solar cell operating voltage is any one of the output current of the solar cell, the output power of the solar cell, the output current of the power converter, and the output power of the power converter. The maximum power control method for a photovoltaic power generation system according to claim 4, wherein the method is proportional to the current value. 6. The solar cell output power at this time is decreased by a predetermined value or more as compared with the previous solar cell output power when the solar cell operation voltage changes with the change of the target solar cell operation voltage at every predetermined time. In this case, the target solar cell operating voltage is lowered regardless of the case where the target solar cell operating voltage is reversed in the rising direction this time. System maximum power control method. 7. The solar cell output power at this time increases by a predetermined value or more as compared with the previous solar cell output power when the solar cell operating voltage changes with the change of the target solar cell operating voltage at every predetermined time. In this case, the target solar cell operating voltage is increased regardless of the case where the target solar cell operating voltage is reversed in the decreasing direction this time. System maximum power control method. 8. A commercial power system connected to the output of the power converter, wherein the control unit detects a system voltage and a system frequency of the commercial power system, and AC power synchronized with the system voltage and the system frequency. While controlling the power converter to generate the, the solar cell operating voltage lower limit value is set in proportion to the system voltage, the target solar cell operating voltage is not lower than the solar cell operating voltage lower limit value. The maximum power control method for the photovoltaic power generation system according to claim 1.