JP2012088916A - Photovoltaic power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photovoltaic power generation system capable of improving the degree of freedom of the system without restricting the number of serially connected solar cell modules.SOLUTION: A photovoltaic power generation system is constituted in such a manner that a plurality of solar cell modules 31, 32, ..., 3m connected in parallel with switches 41, 42, ..., 4m, respectively, are connected in series with each other in addition to a number of solar cell modules 21, 22, ..., 2n in which the open-circuit voltage at the time of low temperature of a solar cell string 11 does not exceed a restriction voltage value, and that each of the switches 41, 42, ..., 4m is opened and the solar cell modules 31, 32, ..., 3m are added one by one according to output voltage decrease of the solar cells.

Description

  The present invention relates to a photovoltaic power generation system.

  Usually, in a photovoltaic power generation system, DC power is generated by using a solar cell string in which a plurality of solar cell modules are connected in series (or a solar cell array in which a plurality of solar cell strings are connected in parallel: the same applies hereinafter) to generate power. The converted direct current power is converted into alternating current power by a power conditioner and supplied to a load such as electrical equipment in a house and a power system.

  In the power conditioner, for example, the maximum input voltage value is determined by the withstand voltage of components constituting the power conditioner such as an electrolytic capacitor and a switching element.

  On the other hand, the output voltage of a solar cell varies depending on the ambient temperature, and the output voltage increases in the morning when the temperature is low, but the output voltage decreases when the ambient temperature rises during the daytime or warms due to self-heating. have. In general, the power conditioner operates at the maximum power point of the solar cell string, but when the power conditioner is stopped, the solar cell string is in a no-load state, and the output voltage of the solar cell string is the maximum power point. The voltage is higher than the voltage at. For this reason, the number of solar cell modules connected in series is limited so that the output voltage of the solar cell string at no load and at a low temperature does not exceed the maximum input voltage of the power conditioner.

  When the inverter is stopped and the solar cell string is in a no-load state, when the input voltage of the power conditioner reaches a preset limit voltage, the switch element in the inverter circuit is turned on to switch A technique for limiting the input voltage of a power conditioner to a limit voltage or less by flowing a load current through the element is disclosed (Patent Document 1).

Japanese Patent Laid-Open No. 2002-10495

  As described above, in the above prior art, the number of solar cell modules connected in series is limited so that the output voltage when the solar cell string is unloaded does not exceed the maximum input voltage of the power conditioner at low temperatures. There was a problem.

  The present invention has been made in view of the above, and it is not necessary to limit the number of solar cell modules connected in series, and to provide a solar power generation system capable of improving the degree of freedom of the system. Objective.

  In order to solve the above-described problems and achieve the object, a photovoltaic power generation system according to the present invention includes a solar cell string configured by connecting a plurality of solar cell modules in series, and a direct current generated by the solar cell string. A power conditioner including an inverter that converts electric power into AC power, and a part of the solar cell modules constituting the solar cell string has a total open voltage per one of the solar cell modules. It is composed of a number equal to or less than a preset limit voltage value, and the rest of the solar cell modules each include a switch connected in parallel with each of the solar cell modules, and the power conditioner includes the power A voltage detector for detecting an input voltage to the conditioner; and based on the input voltage, the inverter A voltage adjustment unit that adjusts the current bus voltage to a preset DC bus voltage setting value, and a switch drive control unit that drives and controls each of the switches in response to a decrease in the input voltage. .

  According to the present invention, there is no need to limit the number of solar cell modules connected in series, and it is possible to improve the degree of freedom of the system.

FIG. 1 is a diagram illustrating a configuration example of the photovoltaic power generation system according to the first embodiment. FIG. 2 is a diagram showing the voltage-power characteristics of the solar cell. FIG. 3 is a flowchart for explaining the solar cell module addition processing in the first embodiment. FIG. 4 is a diagram illustrating another configuration example of the photovoltaic power generation system according to the first embodiment. FIG. 5 is a diagram illustrating still another configuration example of the photovoltaic power generation system according to the first embodiment. FIG. 6 is a diagram of a configuration example of the photovoltaic power generation system according to the second embodiment. FIG. 7 is a flowchart for explaining the solar cell module addition processing in the second embodiment.

  A solar power generation system according to an embodiment of the present invention will be described below with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of the photovoltaic power generation system according to the first embodiment. As shown in FIG. 1, the solar power generation system 1 includes a solar cell string 11 and a power conditioner 5.

  The solar cell string 11 includes solar cell modules 21, 22,..., 2n, 31, 32,..., 3m (n and m are natural numbers) connected in series. Each solar cell module 31, 32,..., 3m is connected in parallel with each switch 41, 42,. Each of the switches 41, 42,..., 4m is preferably a b-contact switch that is controlled to be turned off by an external signal.

  The power conditioner 5 includes a voltage adjustment unit 6, an inverter 7, and a control unit 8. The voltage adjustment unit 6 includes a step-down circuit 61 and a step-up circuit 62. The control unit 8 includes a voltage detection unit 81, a switch drive control unit 82, and a maximum power point tracking control unit 83.

  The DC power from the solar cell string 11 is input to the voltage adjustment unit 6. Based on the input voltage value (input voltage Vs of the power conditioner 5), the voltage adjusting unit 6 to which the DC power is input operates the step-down circuit 61 or the step-up circuit 62 as appropriate, and the DC bus voltage of the inverter 7 is set. It is adjusted to a preset DC bus voltage setting value Vpp and output to the inverter 7. The inverter 7 converts the DC power input from the voltage adjustment unit 6 into AC power.

  The maximum power point tracking control unit 83 controls the voltage adjusting unit 6 and the inverter 7 so that the solar cell string 11 operates at the maximum power point. By this maximum power point tracking control, the input voltage Vs of the power conditioner 5 is controlled to the maximum power point voltage of the solar cell string 11. A known method may be used as the maximum power point tracking control.

  The voltage detector 81 detects the input voltage Vs of the power conditioner 5 and outputs it to the switch drive controller 82.

  The switch drive control unit 82 drives and controls each of the switches 41, 42,..., 4m, for example, one by one in accordance with the decrease in the input voltage Vs of the power conditioner 5 detected by the voltage detection unit 81.

  Here, the change in the output voltage of the solar cell will be described. FIG. 2 is a diagram showing voltage-power characteristics (hereinafter referred to as “VP characteristics”) of the solar cell. In FIG. 2, the horizontal axis represents voltage, and the vertical axis represents the amount of generated power. FIG. 2A shows the VP characteristic when the solar radiation amount is the same and the module temperature changes. The waveform K1 shows the VP characteristic at the reference temperature (for example, 25 ° C.), and the waveform K1 ′ The VP characteristic is shown when the temperature rises due to sunlight or self-heating. FIG. 2B shows a change in the VP characteristic when the amount of solar radiation changes, a waveform K1 shows the VP characteristic when the amount of solar radiation is large, and a waveform K4 shows when the amount of solar radiation is small. VP characteristics are shown. In FIG. 2, points indicated by white circles indicate the maximum power points at which the output power is maximum in each waveform. The voltage at the maximum power point is hereinafter referred to as “maximum power point voltage”. Moreover, the intersection with the horizontal axis of each waveform shows the maximum voltage point in a state where no load, that is, both ends of the solar cell are open. The voltage at this maximum voltage point is hereinafter referred to as “open voltage”.

  When the solar cell material is, for example, single crystal silicon, the change in the output voltage of the solar cell due to the temperature change is a temperature coefficient of about −0.4% / ° C. to −0.5% / ° C. with respect to the temperature rise have. For this reason, as shown in FIG. 2A, when the ambient temperature rises, sunshine or self-heating, for example, when the temperature rises from the reference temperature (25 ° C.) to 60 ° C. to 80 ° C., the output voltage is about 14% to 28% lower.

  On the other hand, as shown in FIG. 2B, the change in the output voltage of the solar cell due to the change in the amount of solar radiation has little fluctuation due to the change in the amount of solar radiation for both the open voltage and the maximum power point voltage.

  In general, the temperature of a solar cell rises rapidly from sunrise to past noon and then gradually falls toward sunset. For this reason, the output voltage of the solar cell rapidly decreases from sunrise to past noon when the temperature is highest, since the output voltage decrease range due to the temperature rise exceeds the output voltage increase range due to the increase in solar radiation, and thereafter Until sunset, the output voltage drop due to the decrease in the amount of solar radiation cancels out the increase in output voltage due to the temperature drop, so the change in the output voltage is small and the output voltage is kept low.

  Therefore, in the present embodiment, the number of solar cell modules 21, 22,..., 2n is set to a number that does not exceed a preset limit voltage value when the open voltage of the solar cell string 11 is low, and the output voltage of the solar cell is set. The solar cell modules 31, 32,..., 3m are configured to be added, for example, one by one in accordance with the decrease. By comprising in this way, it is not necessary to restrict | limit the serial connection number of the solar cell modules which comprise the solar cell string 11, and it becomes possible to improve the freedom degree of a system.

  Next, the operation of the photovoltaic power generation system 1 according to the first embodiment will be described with reference to FIG. 1 and FIG. In order to facilitate the following description, the open circuit voltage and the maximum power point voltage of each of the solar cell modules 21, 22,..., 2n, 31, 32,.

  As shown in FIG. 2 (b), even when the amount of solar radiation is low, the solar cell outputs a large open circuit voltage, and the open circuit voltage of the solar cell string 11 is the power conditioner 5 during the period until power conversion is started. To be applied. At this time, the switch drive control unit 82 controls each of the switches 41, 42,..., 4m to be in an ON state and keeps the solar power generation modules 31, 32,. As a result, the input voltage Vs of the power conditioner 5 before the start of power conversion becomes equal to or lower than the limit voltage value.

  When the voltage adjustment unit 6 and the inverter 7 are activated and power conversion is started, the input voltage Vs of the power conditioner 5 is controlled to the maximum power point voltage of the solar cell string 11.

  Thereafter, as the amount of solar radiation increases, the temperature of each of the solar cell modules 21, 22,..., 2n increases due to an increase in ambient temperature or self-heating, and the maximum power point voltage of the solar cell string 11 (that is, the power conditioner 5 The input voltage Vs) decreases.

  The switch drive control unit 82 estimates an open voltage estimated value of the solar cell string 11 based on the input voltage Vs of the power conditioner 5 detected by the voltage detecting unit 81, and opens the limit voltage value stored in advance. When the difference value obtained by subtracting the estimated voltage value is larger than the open-circuit voltage per solar cell module, each switch is set so that the difference value is less than the open-circuit voltage per solar cell module. 41, 42, ..., 4m are controlled, and solar cell modules 31, 32, ..., 3m are added.

  By controlling in this way, for example, even when an abnormality occurs in the power system, the voltage adjustment unit 6 and the inverter 7 are stopped, and the solar cell string 11 is in a no-load state, the open voltage of the solar cell string 11 is maintained. Below the limit voltage value. If this limit voltage value is the maximum input voltage value of the power conditioner 5, it is possible to prevent the open voltage of the solar cell string 11 from exceeding the maximum input voltage value of the power conditioner 5.

Here, the open circuit voltage estimated value of the solar cell string 11 can be estimated using the following equation (1), for example. In the following equation (1), Vs is an input voltage of the power conditioner 5, Voc is an open voltage per solar cell module, and Vpm is a maximum power point voltage per solar cell module.
Vs × (Voc / Vpm) (1)

Also, the determination formula for the difference value is the following expression (2). In the following equation (2), Vsmax is the maximum input voltage value of the power conditioner 5.
Vsmax−Vs × (Voc / Vpm) ≧ Voc (2)

  Next, a process for adding a solar cell module in the first embodiment will be described with reference to FIG. FIG. 3 is a flowchart for explaining the solar cell module addition processing in the first embodiment.

  When the power conversion is started, the switch drive control unit 82 first determines whether or not the expression (2) is satisfied (step ST101).

  In step ST101, when the expression (2) is not satisfied (step ST101; No), the process returns to step ST101. On the other hand, when the expression (2) is satisfied (step ST101; Yes), the switch drive control unit 82 determines whether or not the switch 41 is in an on state (step ST1021). When the switch 41 is in the on state (step ST1021; Yes), the switch drive control unit 82 controls the switch 41 from the on state to the off state (step ST1031), and returns to the process of step ST101.

  In step ST1021, when the switch 41 is not in an on state (in an off state) (step ST1021; No), the switch drive control unit 82 determines whether or not the switch 42 is in an on state (step ST1022). When the switch 42 is in the on state (step ST1022; Yes), the switch drive control unit 82 controls the switch 42 from the on state to the off state (step ST1032), and returns to the process of step ST101.

  Hereinafter, in step ST101, the solar cell modules 31, 32,..., 3m are added until the expression (2) is not satisfied.

  4 and FIG. 5, the same effect as the configuration shown in FIG. 1 can be obtained. FIG. 4 is a diagram illustrating another configuration example of the photovoltaic power generation system according to the first embodiment. FIG. 5 is a diagram illustrating still another configuration example of the photovoltaic power generation system according to the first embodiment.

  In the configuration shown in FIG. 4, the photovoltaic power generation system 1 a includes a solar cell array 100 including solar cell strings 12, 13,..., 1N (N is a natural number) in addition to the solar cell string 11, and each solar cell string 11. , 12,..., 1N are connected in parallel, and a connection box 9 whose output is connected to the power conditioner 5 is provided. The internal configuration of the solar cell strings 12, 13,..., 1N is the same as that of the solar cell string 11.

  In the configuration shown in FIG. 5, the photovoltaic power generation system 1b does not include the voltage detection unit 81 and the switch drive control unit 82 inside the control unit 8a of the power conditioner 5a, but instead of the connection box 9a. A voltage detection unit 91 having the same function as the voltage detection unit 81 and a switch drive control unit 92 having the same function as the switch drive control unit 82 are provided inside.

  4 and 5, solar cell modules 31 and 32 are provided for each of the solar cell strings 11, 12,..., 1N until step (2) is not satisfied in step ST <b> 101 shown in FIG. 3. ,..., 3m can be added to obtain the same effect as the configuration shown in FIG.

  As described above, according to the photovoltaic power generation system of Embodiment 1, in addition to the number of solar cell modules in which the open-circuit voltage at the time of low temperature of the solar cell string does not exceed the preset limit voltage value, the switches are arranged in parallel. Since a plurality of connected solar cell modules are connected in series, and each switch is opened to add a solar cell module in accordance with a decrease in the output voltage of the solar cell, the number of solar cell modules connected in series The degree of freedom of the system can be improved.

  Also, multiplying the ratio of the open circuit voltage to the maximum power point voltage per solar cell module and the input voltage of the power conditioner at that time, the open circuit voltage estimated value of the solar cell string is calculated, and the limit voltage value Since the solar cell module is added so that the difference value obtained by subtracting the estimated open-circuit voltage from the solar cell module is less than the open-circuit voltage per solar cell module, the output voltage of the solar cell string due to temperature rise Can be made less than the open circuit voltage per solar cell module.

  In addition, by setting the limit voltage value as the maximum input voltage value of the power conditioner, for example, when an abnormality occurs in the power system, the voltage adjustment unit and the inverter are stopped, and the solar cell string is in a no-load state, It is possible to prevent the open voltage of the solar cell string from exceeding the maximum input voltage value of the power conditioner.

  Moreover, since the input voltage of the power conditioner can be kept high, power loss due to boosting can be suppressed.

  Furthermore, since the switch is a b-contact switch, the switch is turned on when each switch is not controlled. For example, even when the power conditioner stops due to an error, the output voltage of the solar cell string is reliably supplied to the power conditioner. Or less than the maximum input voltage.

Embodiment 2. FIG.
In the first embodiment, the example in which the limit voltage value set in advance is the maximum input voltage value of the power conditioner has been described. However, when the input voltage of the power conditioner exceeds the DC bus voltage setting value of the inverter It is essential to provide a step-down circuit. On the other hand, in the second embodiment, the preset voltage limit is set to the inverter DC bus voltage setting value, and the input voltage of the power conditioner is kept below the DC bus voltage setting value, thereby eliminating the need for a step-down circuit. An example will be described.

  FIG. 6 is a diagram of a configuration example of the solar power generation system according to the first embodiment. As shown in FIG. 6, the power conditioner 5 b of the photovoltaic power generation system 1 c according to the second embodiment is the same as that in the first embodiment except that the step-down circuit in the voltage adjustment unit 6 a is omitted. The detailed description thereof will be omitted.

  In the photovoltaic power generation system 1c according to the second embodiment, the number of solar cell modules 21, 22,..., 2n is the number that does not exceed the DC bus voltage setting value of the inverter 7 when the open voltage of the solar cell string 11 is low. deep.

  When the voltage adjustment unit 6 and the inverter 7 are activated and power conversion is started, the input voltage Vs of the power conditioner 5 is controlled to the maximum power point voltage of the solar cell string 11.

  Thereafter, as the amount of solar radiation increases, the temperature of each of the solar cell modules 21, 22,..., 2n increases due to an increase in ambient temperature or self-heating, and the maximum power point voltage of the solar cell string 11 (that is, the power conditioner 5 The input voltage Vs) decreases.

  The switch drive control unit 82 estimates the open circuit voltage estimated value of the solar cell string 11 based on the input voltage Vs of the power conditioner 5 detected by the voltage detection unit 81, and from the DC bus voltage setting value of the inverter 7, When the difference value obtained by subtracting the estimated open-circuit voltage value is larger than the open-circuit voltage per solar cell module, each difference value is less than the open-circuit voltage per solar cell module. The switches 41, 42,..., 4m are controlled to add solar cell modules 31, 32,.

  By controlling in this way, for example, even when an abnormality occurs in the power system, the voltage adjustment unit 6 and the inverter 7 are stopped, and the solar cell string 11 is in a no-load state, the open voltage of the solar cell string 11 is maintained. It is possible to prevent the DC bus voltage setting value of the inverter 7 from being exceeded.

  Furthermore, since the input voltage of the power conditioner 5 can be kept below the DC bus voltage setting value of the inverter 7, a step-down circuit becomes unnecessary.

  FIG. 7 is a flowchart for explaining the solar cell module addition processing in the second embodiment. In the flowchart shown in FIG. 7, the only difference from the flowchart of FIG. 3 described in the first embodiment is the difference value determination process shown in step ST101a.

The determination formula for the difference value in the second embodiment is the following expression (3). In the following expression (3), Vpp is a DC bus voltage setting value of the inverter 7. Vs is an input voltage of the power conditioner 5, Voc is a reference open circuit voltage, and Vpm is a maximum power point voltage per one solar cell module.
Vpp−Vs × (Voc / Vpm) ≧ Voc (3)

  When the power conversion is started, the switch drive control unit 82 first determines whether or not the expression (3) is satisfied (step ST101a).

  In step ST101a, when the expression (3) is not satisfied (step ST101a; No), the process returns to step ST101a. On the other hand, when the expression (3) is satisfied (step ST101a; Yes), the switch drive control unit 82 determines whether or not the switch 41 is in an on state (step ST1021). When the switch 41 is in the on state (step ST1021; Yes), the switch drive control unit 82 controls the switch 41 from the on state to the off state (step ST1031), and returns to the process of step ST101a.

  In step ST1021, when the switch 41 is not in an on state (in an off state) (step ST1021; No), the switch drive control unit 82 determines whether or not the switch 42 is in an on state (step ST1022). When the switch 42 is in the on state (step ST1022; Yes), the switch drive control unit 82 controls the switch 42 from the on state to the off state (step ST1032), and returns to the process of step ST101a.

  Hereinafter, in step ST101a, solar cell modules 31, 32,..., 3m are added until expression (3) is not satisfied.

  Similar to the first embodiment, the configuration shown in FIGS. 4 and 5 may be used except that step-down circuit 61 is omitted. That is, by adding the solar cell modules 31, 32,..., 3m for each of the solar cell strings 11, 12,..., 1N until the expression (3) is not satisfied in step ST101a shown in FIG. The same effect as the configuration shown in FIG.

  As described above, according to the photovoltaic power generation system of Embodiment 2, the output voltage of the solar cell string can be kept below the DC bus voltage setting value by setting the limit voltage value as the DC bus voltage setting value of the inverter. Therefore, in addition to the effect of the first embodiment, an effect that a step-down circuit is not required can be obtained.

  Note that the configuration shown in the above embodiment is an example of the configuration of the present invention, and can be combined with another known technique, and a part thereof is omitted without departing from the gist of the present invention. Needless to say, it is possible to change the configuration.

  As described above, the photovoltaic power generation system according to the present invention is useful as an invention that can improve the degree of freedom of the system without limiting the number of solar cell modules connected in series.

1, 1a, 1b, 1c Solar power generation system 5, 5a, 5b Power conditioner 6, 6a Voltage adjustment unit 7 Inverter 8, 8a Control unit 9, 9a Junction box 11, 12, 13, ..., 1N solar cell string 21 , 22, ..., 2n, 31, 32, ..., 3m Solar cell module 41, 42, ..., 4m Switch 61 Step-down circuit 62 Step-up circuit 81, 91 Voltage detection unit 82, 92 Switch drive control unit 83 Maximum power point tracking control Part 100,200 Solar cell array

Claims (6)

A solar cell string formed by connecting a plurality of solar cell modules in series;
A power conditioner including an inverter that converts the DC power generated by the solar cell string into AC power;
With
A part of the solar cell modules constituting the solar cell string is configured by the number of sheets in which the total open voltage per one of the solar cell modules is equal to or less than a preset limit voltage value, and the solar cell module The remainder of each comprises a switch connected in parallel with each of the solar cell modules,
The inverter is
A voltage detection unit for detecting an input voltage to the power conditioner;
A voltage adjusting unit that adjusts the DC bus voltage of the inverter to a preset DC bus voltage setting value based on the input voltage;
A switch drive control unit that drives and controls each of the switches according to a decrease in the input voltage;
A solar power generation system characterized by comprising: A plurality of solar cell strings in which a plurality of solar cell modules are connected in series; and
A connection box for connecting a plurality of the solar cell strings in parallel to form a solar cell array;
A power conditioner comprising an inverter that converts the DC power generated by the solar cell array into AC power;
With
A part of the solar cell modules constituting the solar cell string is configured by the number of the solar cell modules in which the total open voltage per one of the solar cell modules is equal to or less than a preset limit voltage value, and the plurality of the solar cells The rest of the battery modules each comprise a switch connected in parallel with each of the solar cell modules,
The inverter is
A voltage adjustment unit that adjusts the DC bus voltage of the inverter to a preset DC bus voltage setting value based on the input voltage,
The junction box is
A voltage detection unit for detecting an output voltage to the power conditioner;
A switch drive control unit that drives and controls each of the switches according to a decrease in the output voltage;
A solar power generation system characterized by comprising: The switch drive controller is
Prior to the start of power conversion, the switches are short-circuit controlled, and after the start of power conversion, the ratio of the open voltage to the maximum power point voltage per one of the solar cell modules and the output voltage are multiplied by the output voltage. An open-circuit voltage estimated value of a solar cell string is calculated, and each switch is open-controlled so that a difference value obtained by subtracting the open-circuit voltage estimated value from the limit voltage value is less than the open-circuit voltage. The photovoltaic power generation system according to claim 1 or 2. The limit voltage value is a maximum input voltage value of the power conditioner,
The voltage adjustment unit includes a step-down circuit that steps down the input voltage to the DC bus voltage setting value when the input voltage is equal to or higher than the DC bus voltage setting value, and the input voltage is less than the DC bus voltage setting value. The solar power generation system according to any one of claims 1 to 3, further comprising: a booster circuit that boosts the input voltage to the DC bus voltage set value in some cases. The limit voltage value is the DC bus voltage setting value,
The voltage regulator includes a booster circuit that boosts the input voltage to the DC bus voltage setting value when the input voltage is less than the DC bus voltage setting value. The solar power generation system as described in any one.   Each said switch is b contact switch, The solar power generation system as described in any one of Claims 1-5 characterized by the above-mentioned.

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