JPH11103538A - Optical power generating system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical power generating system that can prevent decrease of power generating efficiency of the whole system. SOLUTION: An optical power generating system 100 comprises a plurality of solar battery modules 1a to 1n, and a plurality of power converters 2a to 2n respectively connected to the modules 1a to 1n and having maximum solar energy pursuing functions. The converters 2a to 2n are connected in series to one another. The modules 1a to 1n have their output current and output voltage controlled by the maximum solar energy pursuing functions of the converters 2a to 2n, so that the maximum power generating efficiency can be always obtained. Further, a common output current flows through the output terminals of the converters 2a to 2n, and the output voltages are automatically adjusted, so that the ratio of any two voltages becomes equal to the ratio of the maximum powers of the corresponding two of the modules 1a to 1n.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic system for converting a voltage and a current output from a photovoltaic power into electric power and outputting the converted electric power to a load or a battery.

[0002]

2. Description of the Related Art In recent years, photovoltaic power generation has been spreading as an applied technology of photovoltaic power generators. In solar power generation, output voltage-output current characteristics of a solar cell change due to natural conditions such as solar radiation intensity and ambient temperature, and aging of the solar cell.
Therefore, so-called maximum power tracking control (MPPT control) is indispensable in order to keep the output voltage and output current of the solar cell at an operating point at which the maximum power can be extracted (optimal operating point).

FIG. 4 is a diagram showing a configuration of a conventional photovoltaic system. As shown in the figure, a plurality of solar cell modules 101a to 101n are connected in series to form a solar cell panel 105, the output of which is connected to a load via a power converter 102 having an MPPT control function. I have. In addition, each of the solar cell modules 101a to 101a
01n, when the power generation capacity is reduced or the power generation is stopped due to the interruption of sunlight or failure due to dirt or shade on the surface of the solar cell module 101a or the like,
Other normally operating solar cell modules 101a-
Diode (bypass diode) 104a serving as a bypass element in order to flow the current output from 101n
To 104n are connected.

[0004]

When power is taken out from the solar cell panel 105 by connecting the solar cell modules 101a to 101n in series as shown in FIG. 4, all the solar cell modules 101a to 101n are connected to the solar cell modules 101a to 101n. The same current flows. This is the same when the MPPT control is performed, and a predetermined output current value is set so that the maximum power can be obtained as a whole of the solar cell panel 105.
However, the optimum operating points of the respective solar cell modules 101a to 101n are different from each other due to differences in light incident conditions and characteristics, and all the solar cell modules 101a to 101n operate at the same operating current at the same output current value. I can't let that happen. That is, all the solar cell modules 101a to 101n constituting the solar cell panel 105
Since the optimum operating point cannot be determined so that the maximum power can be extracted from the solar cell modules, the maximum power generation capacity of each of the solar cell modules 101a to 101n cannot be simultaneously extracted.

In order to prevent such a decrease in power generation efficiency, the output voltages V1 to Vn of the solar cell modules 101a to 101n are connected to the respective solar cell modules 101a to 101n.
01n may be controlled so as to be the optimum operating point. FIG. 5 is a diagram illustrating a configuration of a power generation control device that variably controls output voltages Va to Vn of a plurality of solar cell modules 101a to 101n connected in series. As shown in the figure, the solar cell modules 101a to 101n include:
Each of the switching elements 106a to 106n is connected. This power generation control device can control the ratio of the output voltage by changing the off duty (the ratio between the on / off cycle of the switching element and the off period) Da to Dn of each of the switching elements 106a to 106n. ..: Vn = Da: Db:...: Dn. That is, the off-duties Da to D
n to control all the solar cell modules 101a
By setting the respective output voltages V1 to Vn so that the power supply voltages of the solar cell modules 101a to 101n can operate at the optimum operation point, it is possible to extract the maximum power from the solar cell modules 101a to 101n.

However, in the above-described power generation control device, the off duty of each of the switching elements 106a to 106n must be controlled to a different value, so that the control method becomes complicated. Also, each solar cell module 101a
If the number of the photovoltaic modules 101a and the like is changed in advance, the number of the photovoltaic modules 101a and the like need to be determined in advance if the number of the photovoltaic modules 101a and the like is changed. The ratio has to be changed, and there is a problem that the configuration is inflexible.

[0007] The present invention has been made in view of the above points, and an object of the present invention is to provide a photovoltaic power generation system capable of preventing a reduction in power generation efficiency of the entire system.

[0008]

In order to solve the above-mentioned problems, a photovoltaic power generation system according to the present invention includes a plurality of photovoltaic power generators for converting light energy into electric energy, and each of the photovoltaic power supplies is connected to each of the photovoltaic power generators. And a plurality of power converters having a maximum power tracking function. These power converters are connected in series. Each power converter controls the voltage and current output from the photovoltaic power generator so that the maximum power tracking function can extract the maximum power from the connected photovoltaic power generator. As described above, the operating point (optimum operating point) at which the maximum power can be extracted from each photovoltaic power generator differs for each photovoltaic power generator. Are controlled so as to always generate the maximum power separately, so that it is possible to prevent a decrease in the power generation efficiency of the entire photovoltaic power generation system. Furthermore, the power generation efficiency of each photovoltaic unit is controlled by the maximum tracking function of the power converter, and is not affected at all by fluctuations in the power generation efficiency of other photovoltaic units. Therefore, even when the number of photovoltaic power generators is changed, each photovoltaic power generator can always be operated at the optimum operating point, and a flexible photovoltaic power generation system can be realized.

In addition, a photovoltaic power generation system that can obtain more generated power can be constructed by connecting the power generation modules having the above-described configuration in parallel. In such a photovoltaic power generation system, each power generation module performs a power generation operation separately, and the photovoltaic elements in each power generation module operate at an optimum operating point, thereby preventing a decrease in power generation efficiency of the entire photovoltaic power generation system. be able to.

The photovoltaic element described above is, specifically, a solar cell module in which solar cells are combined, or a solar cell panel in which a plurality of solar cells are further combined so that the maximum power can be taken out in units of these. Is controlled. In particular, by operating each solar cell module at the optimum operating point, it is possible to minimize a decrease in the power generation efficiency of the entire photovoltaic power generation system. In addition, the configuration can be simplified by operating at the optimum operating point for each of the larger solar cell panels.

The above-mentioned power converter is a DC / DC converter having a maximum power tracking function, and the entire output voltage (each of which is applied to a load) while each photovoltaic element is operated at an optimum operating point. The maximum output current can flow while keeping the sum of the output voltages of the power converters constant. Therefore, the power generation amount of the photovoltaic power generation system is always the sum of the maximum power generation amounts of the individual photovoltaic power generation bodies, and it is possible to prevent a reduction in power generation efficiency due to differences in the characteristics and sunshine state of each photovoltaic power generation body.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a photovoltaic power generation system according to an embodiment of the present invention, a power converter having an MPPT control function is connected to each of a plurality of solar cell modules, and each of the solar cell modules operates optimally. It is characterized in that control is performed so as to operate (generate power) at a point. Hereinafter, regarding the photovoltaic power generation system of one embodiment to which the present invention is applied,
This will be specifically described with reference to the drawings.

(1) Overall Configuration of Photovoltaic System FIG. 1 is a diagram showing the overall configuration of a photovoltaic system according to an embodiment to which the present invention is applied. As shown in the figure, the photovoltaic system 100 includes a plurality of solar cell modules 1a to 1a.
1n, a plurality of power converters 2a to 2n, and a reverse current prevention diode 3. The photovoltaic system 100 shown in FIG. 1 includes a battery device 10 and other electric devices (not shown) connected as electric loads.
The description will be made on the assumption that these electric loads are sufficiently large and the maximum output current generated by performing the MPPT control always flows through these electric loads.

Each of the solar cell modules 1a to 1n is composed of a plurality of solar cells (PV cells) connected in series or in parallel. A PV cell has, for example, a shape in which a thin N-type semiconductor layer is stacked on a thin P-type silicon semiconductor layer. When light is applied, a positive electromotive force is applied to the P-type layer and a negative electromotive force is applied to the N-type layer. Occurs. This power is collected through electrodes formed on the front and back surfaces of the layer.

The solar cell modules 1a to 1n are
Each is connected to the power converters 2a to 2n. The first-stage power converter 2a has one output terminal connected to the plus terminal of the battery device 10 via the reverse current prevention diode 3, and the other output terminal connected to the output terminal of the next-stage power converter 2b. Have been. Each of the power converters 2b to 2m has one output terminal connected to the output terminal of the preceding stage, and the other output terminal connected to the output terminal of the next stage. The final stage power converter 2n has one output terminal connected to the output terminal of the previous stage power converter 2m, and the other output terminal connected to the minus terminal of the battery device 10.

The reverse current prevention diode 3 has a reverse current when the power generation capacity of the photovoltaic power generation system 100 is reduced due to interruption of sunlight or a failure, and the output voltage thereof becomes lower than the voltage between terminals of the battery device 10. It is for preventing.

(2) Detailed Configuration and Operation of Power Converter Next, a detailed configuration and operation of the power converters 2a to 2n shown in FIG. 1 will be described. Each power converter 2a to 2n
Have the same configuration, and the power converter 2a will be described as a representative. FIG. 2 is a diagram illustrating a configuration of the power converter 2a. As shown in the figure, the power converter 2a includes a current sensor 21, a voltage sensor 22, an MPPT control unit 23, and a step-down chopper circuit unit 24.

The current sensor 21 detects the current value flowing from the solar cell module 1a connected to the power converter 2a as M
The voltage is output to the PPT control unit 23, and the voltage sensor 22 outputs the voltage value applied from the solar cell module 1a connected to the power converter 2a to the MPPT control unit 23. MPP
The T control unit 23 changes the ratio between the on time and the off time of the switching element 25 in the step-down chopper circuit unit 24 at regular time intervals.

The step-down chopper circuit section 24 is a DC / DC converter, and controls the ratio of the on-time to the off-time of the switching element 25 in accordance with an instruction from the MPPT control section 23, so that the output voltage becomes the input voltage. It is set in the following range. Further, the input current of the step-down chopper circuit section 24 can be controlled by changing the ratio of the on-time to the off-time of the switching element 25. When the solar cell module 1a is operating near the optimum operating point, By changing this input current, the input voltage (output voltage of the solar cell module 1a) also changes in conjunction with this. These changes in the input current are detected by the current sensor 21 and transmitted to the MPPT control unit 23, and the changes in the input voltage are detected by the voltage sensor 22 and transmitted to the MPPT control unit 23.

The MPPT control unit 23 calculates the power input from the solar cell module 1a to the power converter 2a based on the input current and the input voltage, and calculates the power (the ratio between the ON time and the OFF time of the switching element 25). Is compared with the calculated value of the power (before changing), and the ratio of the ON time and the OFF time of the switching element 25 is changed in the direction of increasing the power. Specifically, the input power is compared as follows, and the ratio of the on time and the off time of the switching element 25 is changed.

FIG. 3 is a characteristic diagram showing the relationship between the output voltage and the output power of the solar cell module 1a. For example, when operating at the point A shown in FIG.
When the operating point moves to the point B by controlling the switching element 25, since the output power has increased, the operating state at the point B having a larger power value is maintained. When the operating point shifts to the point C by controlling the switching element 25 while operating at the point B, the output power is reduced. Controls the switching element 25 again to return the operating point to the point B.

As described above, the MPPT control unit 23 changes the ratio of the ON time to the OFF time of the switching element 25 at regular time intervals, and monitors the increase or decrease of the input power of the solar cell module 1a each time. , So that the output power of the solar cell module 1a is always maximum, that is,
The control is performed so that the solar cell module 1a operates at the optimum operation point. Further, since the power input to the power converter 2a is maximum, the power output from the power converter 2a is also maximum.

Next, the voltage and current output from power converters 2a to 2n will be considered. In FIG. 1, the maximum power output from the solar cell modules 1a to 1n is P1 to Pn, the power output from the power converters 2a to 2n is P1 'to Pn', and the power converters 2a to 2n.
The voltages output from 2n are denoted by V1 to Vn, the terminal voltage of the battery device 10 is denoted by VB, and the current flowing through an electric load such as the battery device 10 is denoted by I.

Assuming that the power loss in each of the power converters 2a to 2n is zero, the following relationship holds: P1 = P1 ', P2 = P2',..., Pn = Pn '. The voltage VB and the current I are represented by the following equations.

VB = V1 + V2 +... + Vn (2) I = P1 / V1 = P2 / V2 =... = Pn / Vn (3) In the equation (3), the power converters 2a to 2n are connected in series. Output voltage V of each of power converters 2a-2n
1 to Vn are proportional to the output powers P1 to Pn of the corresponding solar cell modules 1a to 1n, and each output voltage V1 to Vn
This shows that the ratio of Vn is controlled to be equal to the ratio of each of the solar cell modules 1a to 1n.

For example, when only the solar cell module 1a enters the shade and the output power P1 decreases, the voltage and current that have been shared by the solar cell module 1a cannot be maintained. 1n
Under the condition that the output current of the power converter 2a becomes constant, the respective power converters 2a satisfy the above-described equations (1) to (3).
2n and output currents I common to them are automatically set. Actually, the power converter 2a connected to the solar cell module 1a having reduced power generation capacity
, The output voltage V1 of the power converter 2b and the like increases. Further, as can be seen from the fact that the output voltages V2 and the like other than the solar cell module 1a increase, the common output current I decreases. Although the output voltage and the output current of each power converter 2b and the like change in this way, the solar cell modules 1b and the like connected to the respective input sides are separately subjected to the MPPT control, so that the optimum operation is always performed. The operation at the point is maintained, and the maximum power at that time is obtained.

As described above, in the photovoltaic power generation system 100 of the present embodiment, the power converters 2a to 2n having the MPPT control function are connected to the solar cell modules 1a to 1n, respectively. The output terminals are connected in series to obtain the entire output voltage. Therefore, each of the solar cell modules 1a to 1n can be operated at the optimum operating point by separately performing the MPPT control.
A decrease in the power generation efficiency as a whole can be prevented.

A common output current I flows through the output terminals of the power converters 2a to 2n, and each of the solar cell modules 1a to 2n.
Since the output voltages Va to Vn of the power converters 2a to 2n are automatically adjusted so as to be equal to the ratio of the maximum power output from 1n, there is no need to perform complicated control. Also,
Even if the power generation capacity of any of the solar cell modules 1a to 1n is reduced due to shadow or dirt, or due to aging or variation in the original characteristics, the maximum power can be obtained in each of the solar cell modules 1a to 1n. Since the output voltage and output current of each of the power converters 2a to 2n are automatically adjusted, there is no influence on other solar cell modules,
It is possible to minimize a decrease in generated power of the entire photovoltaic power generation system 100.

The same applies to the case where the number of solar cell modules and power converters increases or decreases. Each output voltage and output current of the power converter are controlled while operating each solar cell module at the optimum operating point. Since the adjustment is automatically performed, it is easy to change the system configuration according to the magnitude of the electric load, and a flexible photovoltaic system can be realized.

As described above, each of the solar cell modules 1a to 1n may have a different power generation capability. Therefore, the photovoltaic power generation is performed by intentionally changing the installation conditions of each of the solar cell modules 1a to 1n. It is also easy to adjust the time change of the power generation characteristics of the entire system 100.

In a large-scale photovoltaic power generation system, the number of solar cell panels in which a plurality of solar cell modules are connected in series is increased, a power converter is installed for each solar cell panel, and the output side is connected in parallel. By connecting, the same effect as the photovoltaic power generation system 100 of the present embodiment can be obtained, but the photovoltaic power generation system 100 is also suitable for a small-scale home system having a small number of solar cell modules 1a and the like.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, in the above-described embodiment, the power converters 2a to 2n are connected to each of the solar cell modules 1a to 1n. However, a plurality of solar cell modules constitute a solar cell panel, and each of the solar cell panels performs power conversion. The power converters may be connected so that each power converter is connected in series and connected to an electric load.

The photovoltaic power generation system 100 shown in FIG.
Is not connected to an electric load such as the battery device 10 alone, but a plurality of power generation modules having the same configuration as the photovoltaic power generation system 100 shown in FIG. You may make it connect to a load. In this case, since each power generation module operates independently, the solar cell module 1a and the like included in each power generation module can be operated at the optimum operation point, so that a decrease in the power generation efficiency of the entire photovoltaic power generation system can be prevented. it can.

In the above-described embodiment, the voltage and current output from the solar cell module 1a and the like are monitored and
Although the PPT control is performed so that the solar cell module 1a and the like can generate power at the maximum efficiency, the control may be performed by another method. For example, MPPT control may be performed by monitoring the voltage and current output from the power converter 2a and the like. In this case, the current sensor 21 and the voltage sensor 22 may be provided in the output stage of the power converter. Focusing on the fact that the voltage output from the solar cell module 1a and the like varies little and the output current greatly varies depending on the ambient temperature, the output current-temperature characteristics of the solar cell module 1a and the like are stored in advance. The MPPT control may be performed by monitoring the temperature around the solar cell module 1a or the like. In the above-described embodiment, the step-down chopper circuit unit 24 is used for the power converter 2a and the like, but a step-up chopper circuit may be used.

Further, in the above-described embodiment, the battery device 10 is connected to a stage subsequent to the plurality of power converters 2a to 2n connected in series. However, a boost type power converter ( (DC / DC converter). As described above, in the photovoltaic power generation system of the present embodiment, when the power generation capacity of each solar cell module 1a or the like decreases, the output voltage of the corresponding power converter 2a or the like relatively decreases. When the number of the power converters 2a and the like whose output voltage is reduced increases, the voltage applied to the battery device 10 may decrease and supply of power may be stopped. However, by inserting a step-up type power converter, this decrease in output voltage can be compensated for, so that the operating range can be expanded.

[0036]

As described above, according to the present invention, a power converter having a maximum power tracking function is connected to each of the photovoltaic power generators constituting the photovoltaic power generation system. They are connected in series. For this reason, since the maximum power tracking function of the power converter is controlled so that each photovoltaic unit always always outputs the maximum power, a decrease in the power generation efficiency of the entire photovoltaic system can be prevented. Furthermore, the power generation efficiency of each photovoltaic unit is controlled by the maximum tracking function of the power converter, and is not affected at all by fluctuations in the power generation efficiency of other photovoltaic units. Therefore, even when the number of photovoltaic power generators is changed, each photovoltaic power generator can always be operated at the optimum operating point, and a flexible photovoltaic power generation system can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a photovoltaic power generation system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a power converter.

FIG. 3 is a diagram showing output voltage-output power characteristics of a solar cell module.

FIG. 4 is a diagram showing a configuration of a conventional photovoltaic power generation system.

FIG. 5 is a diagram showing a configuration of a power generation control device using a solar cell module to which switching elements are connected.

[Explanation of symbols]

 1a to 1n Solar cell module 2a to 2n Power converter 3 Reverse current prevention diode 10 Battery device 21 Current sensor 22 Voltage sensor 23 MPPT control unit 24 Step-down chopper circuit unit 25 Switching element 100 Photovoltaic power generation system

Claims (5)

[Claims] 1. A plurality of photovoltaic units for converting light energy into electric energy, and a plurality of photovoltaic units connected to each of the plurality of photovoltaic units and having a maximum power tracking function for extracting maximum power from the corresponding photovoltaic units. A photovoltaic power generation system comprising: a power converter; and a plurality of the power converters connected in series. 2. A photovoltaic power generation system in which a plurality of power generation modules are connected in parallel, wherein each of the power generation modules includes a plurality of photovoltaic elements for converting light energy into electric energy, and an input terminal connected to the plurality of photovoltaic power generation modules. A plurality of power converters connected to each of the bodies and having output terminals connected in series with each other and having a maximum power tracking function for extracting maximum power from the corresponding photovoltaic power generator. 3. The photovoltaic power generation system according to claim 1, wherein the photovoltaic element is a photovoltaic module in which photovoltaic cells are combined. 4. The photovoltaic power generation system according to claim 1, wherein the photovoltaic element is a solar cell panel in which a solar cell module is combined. 5. The photovoltaic power generation system according to claim 1, wherein the power converter is a DC / DC converter.