JP2001223377A - Snow-melting controlling method for photovoltaic power generation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent snow-melting controlling method for a photovoltaic power generation apparatus whereby a stable snow melting work can be performed. SOLUTION: A controlling means 7 has reverse-current preventing diodes each of which is interposed between each solar battery string and a bidirectional power converting means 3, bypass electric lines each of which is interposed between the terminals of each reverse-current preventing diode, and switches for opening/closing the respective bypass electric lines. When melting a snow, electric power are so applied intermittently from the bidirectional power converting means 3 to the one or more solar battery strings by opening/closing the switches that all the respective switches are not brought into open states at the same time, while the electric power are applied intermittently to the plurality of solar battery strings.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling snow melting of a photovoltaic power generator having a snow melting function.

[0002]

2. Description of the Related Art It has been widely known that a solar cell is heated to generate heat and melt ice and snow attached to a light receiving surface of the solar cell, that is, so-called snow melting, by energizing the solar cell. For example, in a solar power generation device configured to charge a storage battery with power generated by a solar battery via a backflow prevention diode, when ice and snow are deposited on the solar battery, the backflow prevention diode is bypassed and the solar battery is bypassed by the storage battery. There has been proposed an apparatus configured to apply a forward bias voltage to a battery and apply a heating current to melt the ice and snow (see, for example, Japanese Patent Application Laid-Open No. 62-254635).

Further, in a system interconnection system in which a solar cell and a commercial power supply are connected, a plurality of solar cell strings in which a plurality of solar cells are connected in series are connected in parallel, and There is also known a device using a bidirectional power conditioner having both a power conversion function at the time of string power generation and a power conversion function at the time of melting snow and ice attached to solar cells (for example, Japanese Patent No. 2749959, Kaihei 10-
271860, JP-A-10-285966, etc.).

FIG. 5 shows an example of a photovoltaic power generator having a snow melting function using a bidirectional power conditioner. As shown in FIG. 5, solar cell strings 1a, 1b, 1c in which a plurality of solar cells (modules or cells) are connected in series.
Are connected in parallel to a junction box 2 provided with a backflow prevention diode, a surge protection component and a breaker, and are connected to a bidirectional power conditioner 3 capable of performing forward conversion and reverse conversion and the AC power supply 4 side.

Here, at the time of power generation of the solar cells, the DC power generated by each of the solar cell strings 1a, 1b, 1c is converted into AC by the bidirectional power conditioner 3,
Reverse power flow to AC power supply 4 side.

On the other hand, during the snow melting operation, the AC power from the AC power supply 4 is converted into DC by the bidirectional power conditioner 3, and the solar cell strings 1a, 1b, 1c are energized in the forward direction. Snow melting is performed by causing the solar cell to generate heat.

At this time, in order to bypass the backflow prevention diode of each of the solar cell strings 1a, 1b, 1c provided in the connection box 2, switching means and the like are installed and bypassed. This switching means can be mechanical relay contacts,
Semiconductor elements such as power transistors, FETs, and IGBTs are used.

In the snow melting control using the bidirectional power conditioner 3, since the conventional conversion control at the time of power generation can be used as it is, the control and protection of voltage, current and electric power at the time of snow melting are also performed. Can be performed.

[0009]

However, in a conventional snow melting control method for a photovoltaic power generator using a bidirectional power conditioner, a so-called constant voltage control in which control is performed while applying a constant voltage to a solar cell is generally performed. Since the current of a solar cell greatly changes due to a slight change in temperature, the current and the power greatly change due to variations in the characteristics of the solar cells constituting one solar cell string and slight changes in the characteristics due to a change in temperature. As a result, stable control is difficult, and a protection circuit for preventing overcurrent is separately required.

In addition, even when a constant current or constant power control is performed, especially when a plurality of solar cell strings are connected in parallel, the voltage of each solar cell string becomes common, so that the characteristic of each solar cell string is reduced. Due to the variation and the difference in the state of snow, the current varies between the solar cell strings. As a result, there is a problem that the energized power density varies for each string.

For this reason, it is sufficient to perform constant current and constant power control for each solar cell string. However, when a converter control circuit is provided for each solar cell string, there is no merit of using a bidirectional power conditioner. ,
The method of providing a current limiting resistor and a semiconductor element for each solar cell string has a problem that heat loss is large and cannot be an efficient snow melting control method.

Further, when the solar cell is actually installed on a roof surface or the like, appropriate heat generation is required depending on the purpose of use, such as snowfall or snow melting provided with snow stoppers, or the installation position such as an eaves part, a ridge part, or a central part. Although the degree differs, the heat generation ability cannot be set for each string by the conventional method.

In addition, it is not possible to select a snow-proof operation or a partially concentrated operation in which the entire roof is uniformly heated according to the snowfall situation.

In addition, when the energization is switched sequentially for each single solar cell string, a large current is opened and closed, and there is a concern that noise may be generated, and at the moment of the switching, the power supply may be shut down due to interruption of energization. Can be considered.

For the detection of the power generation possible state, it is easiest to detect the open-circuit voltage of the solar cell string. However, in order to detect the open-circuit voltage of the solar cell string, it is necessary to stop energizing the power supply itself. Is stopped, the problem of the beat and the noise described above can be considered.

Accordingly, an object of the present invention is to solve the conventional problems described above and to provide an excellent snow melting control method for a photovoltaic power generator capable of performing a stable snow melting operation.

[0017]

In order to solve the above-mentioned problems, a method for controlling snow melting of a photovoltaic power generator according to the present invention comprises a solar cell array in which a plurality of solar cell strings in which solar cells are connected in series are connected in parallel. A method for controlling snow melting of a photovoltaic power generator, wherein the method is connected to bidirectional power conversion means capable of performing forward conversion and reverse conversion via a control means, and the bidirectional power conversion means is connected to an AC power supply. The means includes a backflow prevention diode interposed between each solar cell string and the bidirectional power conversion means, a bypass circuit provided between terminals of each backflow prevention diode, and a switch for opening and closing each bypass circuit. At the time of snow melting, the switch is opened and closed to intermittently supply electric power to one or more solar cell strings from the bidirectional power conversion means. Chi is characterized in that all was as not to open at the same time.

Further, the opening / closing control of the switch selected especially during snow melting is performed according to the heat generation degree of the solar cell string.

The control means includes means for detecting an open-circuit voltage or a short-circuit current in each solar cell string. The open-circuit voltage or the short-circuit current detected during the power-supply interruption period of the solar cell string corresponding to the switch selected during snow melting is provided. When the value is equal to or larger than the set value, the solar cell string is excluded from the target of the intermittent energization.

When the number of intermittently energized solar cell strings is one, the output from the bidirectional power conversion means is kept at a constant voltage for a predetermined period of time, and the power generation possible state is determined from a change in the energizing current of the solar cell strings. It is characterized by the following.

Further, in the case where there is one solar cell string which is intermittently energized, the solar cell strings excluded from the intermittent energization are intermittently energized for a predetermined time to detect a power generation enabled state.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram illustrating an embodiment of a photovoltaic power generator (system) S according to the present invention. A solar cell string 1a, in which a plurality of solar cells (solar cell modules or solar cell elements) are connected in series at least.
Reference numerals 1b and 1c denote bidirectional power conversion means which are connected in parallel to a circuit in a snow melting control box (control means) 7 having a built-in switching control circuit 12 for controlling these energization switching, and which can perform forward conversion and reverse conversion. It is connected to an AC power supply 4 which is a system power supply via a bidirectional power conditioner 3 and is connected to the system. As shown in the figure, a remote controller 14 may be attached for snow melting operation.

Here, the control box 7 for snow melting
Are provided with branch switches 11a, 11b, 11 for maintenance and inspection etc. in each of the solar cell strings 1a, 1b, 1c.
c and the backflow prevention diodes 5a, 5b, 5c. In addition, each solar cell string has a bypass circuit 13 for bypassing between the terminals of the backflow prevention diode.
a, 13b, and 13c are provided, and switches (6a, 6b, and 6c) each including a switching element and the like are provided in each bypass electric circuit (13a, 13b, and 13c). A surge absorber 9 for surge protection due to lightning or the like and a main switch 10 are provided between the bypass circuit and the bidirectional power conditioner 3. Further, the switching control circuit 12 controls the opening and closing of the switches 6a, 6b, 6c.
In addition, you may make it provide each said circuit element on one circuit board.

The photovoltaic power generator configured as above is
Ice and snow attached to the light receiving surface side of the solar cell is melted as follows. First, at the time of power generation, the solar cell strings 1a, 1
The DC power generated by b and 1c is converted into AC by the bidirectional power conditioner 3, and the reverse power flows to the AC power supply 4 side. During the snow melting operation, the AC power from the AC power source 4 is converted into DC by the bidirectional power conditioner 3 and the solar cell strings 1a, 1b, 1c are energized in the forward direction. The snow melting is carried out by causing the solar cell constituting the device to generate heat.

When constant current control is performed by the bidirectional power conditioner 3, the current value determines the snow melting power of the total solar cell array (solar cell string 1a + solar cell string 1b + solar cell string 1c). The current value is set according to the system capacity and the rated capacity of the bidirectional power conditioner 3.

Rotation energization (intermittent energization) is applied to each of the solar cell strings 1a, 1b, 1c in a forward direction with a constant current for a short time (from the order of 100 ms to several tens of minutes). For example, the rotation is performed in the order of 1a → 1b → 1c → 1a →. In this case, stable control is possible because of constant current control. Each string is energized by a voltage corresponding to the number of series. At this time, the energizing time of each solar cell string (switches 6a, 6b, 6c)
(ON (closed) time) ta, tb, tc are set in advance in advance, and can be appropriately changed according to installation conditions and use conditions.

Here, if the rotation cycle (intermittent cycle) is as short as about several seconds, the temperature of each solar cell string does not change greatly according to the ON / OFF control of the power supply. ta, tb, tc
Then, the degree of heat generation of each solar cell string can be adjusted by calculating from the energization timing of each solar cell string.

FIG. 2 shows an example of a time chart of each solar cell string. An energization overlap time tj is provided so that the OFF time of the solar cell string 1a (corresponding to the opening time of the switch 6a) does not overlap with the OFF time of the solar cell string 1b (corresponding to the opening time of the switch 6b). 1c is the same time chart as the solar cell string 1b. In this case, the solar cell strings 1b and 1c have the same heat generation degree. If tj is short, the heat generation degree 1a: 1b (= 1)
c) = ta: tb (= tc) / 2.

As described above, the opening and closing of the switch is controlled in accordance with the degree of heat generation of the solar cell string.
For example, it is possible to set the heat generation capacity for each solar cell string even when the appropriate heat generation degree differs at the installation position of the solar cell string such as the eaves part, the ridge part, the central part, etc., so that efficient snow melting can be performed. Can be.

Further, in order to perform efficient snow melting, it is desired that when the snow melting is completed and the power generation becomes possible, the snow melting operation is automatically stopped and the operation is shifted to the power generation operation. Since a solar cell also serves as a sensor that generates voltage by light, if the open-circuit voltage detection value or short-circuit current value of a specific solar cell string exceeds a set value, it can be determined that the solar cell string can generate power. it can.

As described above, in the method for controlling snow melting of the photovoltaic power generator according to the present invention, a pause period occurs during the energization of each solar cell string.
The open-circuit voltage and short-circuit current of the solar cell string can be detected without affecting the snow-melting operation at all and without stopping the bidirectional power conditioner 3.

As shown in FIG. 3, when the detected value exceeds a power generation possibility judgment value set in advance for each solar cell string, it is determined that power generation is possible. The strings determined to be capable of generating power stop intermittent energization. As a result, current can be concentrated and supplied to the remaining solar cell strings that have not completed snow melting, and efficient snow melting can be achieved. In addition, regarding the determination of the power generation possible state of the last remaining solar cell string, the DC output voltage limit value of the bidirectional power conditioner 3 is reduced to the vicinity of the power generation possible determination value at regular intervals (from several minutes to several tens of minutes). Thus, the control is switched to the constant voltage control for a short time. At this time, if the last remaining solar cell string can generate power, as shown in FIG. 4, since the open-circuit voltage has reached the power generation feasibility determination value, the direction of the energizing current is reversed. The determination can be made by detecting the DC output power or current of the bidirectional power conditioner 3.

As another method, power supply may be switched to the solar cell strings excluded from the power supply rotation for a few seconds at regular intervals, and power generation possibility detection may be performed as in the case of intermittent power supply of a plurality of strings.

When the detected values of all the solar cell strings finally become equal to or higher than the power generation possible determination value, it can be determined that the snow melting has been completed and the power generation is possible, so the snow melting operation is stopped and the bidirectional power conditioner is stopped. 3 is shifted to the power generation operation.

In the method of controlling the photovoltaic power generation device with a snow melting function according to the present invention, it is possible to easily change the energizing time of each solar cell string of the intermittent energizing, so that the optimal snow melting control according to various situations is possible. .

For example, if the energizing time of each intermittently energized solar cell string is adjusted in order to prevent snow accumulation from the beginning of snowfall, the entire solar cell array can be uniformly warmed and a snow-proof operation can be performed. . At this time, the time of the intermittent energization of each solar cell string may be changed by setting a snow-proof operation switch for manual operation, or automatically using a snow-fall sensor or the like when the snow-fall is detected. It is also possible to set to enter the mode.

Further, when the apparatus is actually installed on a roof or the like, the purpose of use such as falling snow or snow melting provided with snow stoppers, the eaves part,
It is natural that the appropriate degree of heat generation differs depending on the installation position such as the ridge and the center.

For example, if the purpose is to make snow fall, it is conceivable to concentrate the electric power particularly on the eaves and the ridge according to the arrangement of the solar cell array. Specifically, when the degree of heat generation is to be set to eaves top part: center part: ridge part = 3: 1: 3, (power supply current) × (power supply time) is obtained from the power supply timing of each solar cell string and the power supply time of intermittent power supply. 3:
Ta, tb, and tc may be set so as to be 1: 3.

Of course, this ON / OFF time setting
Instead of being calculated and entered by the user each time, several pre-set items such as snowfall, snowmelt, snow protection, user settings, etc. are automatically operated using buttons or the like or using a snowfall sensor or snowfall sensor. In driving, it is preferable to call up an appropriate setting.

[0041]

As described above in detail, according to the method for controlling snow melting of a photovoltaic power generator according to the present invention, it is possible to perform extremely stable snow melting control with as little influence as possible due to variations in characteristics of solar cells. In addition, a protection circuit for preventing overcurrent is not required.

Further, since the degree of heat generation can be freely changed for each solar cell string according to the purpose of use, installation location, etc., it is possible to perform optimal snow melting control according to various situations.

Furthermore, since the power generation possible state of the solar cell can be detected and the operation can be automatically shifted to the power generation operation, efficient snow melting and power generation can be realized.

When the power generation possible state of the solar cell is detected, when detecting the open voltage of the solar cell string, there is no need to stop energization, and an excellent solar power free from worries or noises of the power supply. A photovoltaic device can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an embodiment of a solar power generation device according to the present invention.

FIG. 2 is a time chart showing the energization control of the photovoltaic power generator according to the present invention.

FIG. 3 is a voltage-current characteristic diagram relating to detection of possible power generation of a solar cell string.

FIG. 4 is a voltage-current characteristic diagram relating to determination of a power generation possible state of a solar cell string that performs a snow melting operation last.

FIG. 5 is a diagram illustrating an example of a conventional solar power generation device, and is a schematic configuration diagram schematically illustrating a state of electrical connection.

[Explanation of symbols]

1a, 1b, 1c: Solar cell string 2: Connection box 3: Bidirectional power conditioner (bidirectional power conversion means) 4: AC power supply 5a, 5b, 5c: Backflow prevention diode 6a, 6b, 6c: Switch 7: Snow melting Control box (control means) 8: Operation remote controller 9: Surge absorber 10: Main switch 11: Branch switch 12: Switching control circuit 13a, 13b, 13c: Bypass circuit S: Photovoltaic power generator (system)

Claims (5)

[Claims] A solar cell array in which a plurality of solar cell strings in which solar cells are connected in series is connected to bidirectional power conversion means capable of forward conversion and reverse conversion via a control means. A method for controlling snow melting of a photovoltaic power generator, comprising connecting power conversion means to an AC power supply, wherein the control means includes a backflow prevention diode interposed between each solar cell string and the bidirectional power conversion means. A bypass circuit provided between the terminals of the backflow prevention diodes, and a switch for opening and closing each bypass circuit. When snow melts, the switch is opened and closed to supply power from the bidirectional power conversion means to one or more solar cell strings. The intermittent power supply is performed while the plurality of solar cell strings are intermittently supplied with power, so that all of the switches are not simultaneously opened. A snow melting control method for a photovoltaic device. 2. The snow melting control method for a photovoltaic power generator according to claim 1, wherein the control of opening and closing the switch selected at the time of snow melting is performed in accordance with the degree of heat generation of the solar cell string. 3. The control means includes means for detecting an open-circuit voltage or a short-circuit current in each solar cell string, wherein the open-circuit voltage or short-circuit detected during a power supply suspension period of the solar cell string corresponding to the switch selected during the snow melting. The method according to claim 1, wherein when the current is equal to or more than a set value, the solar cell string is excluded from a target of the intermittent energization. 4. When the number of the intermittently energized solar cell strings is one, the output from the bidirectional power conversion means is kept at a constant voltage for a predetermined time, and a power generation possible state is determined from a change in energizing current of the solar cell strings. The method according to any one of claims 1 to 3, wherein the snow melting control method is performed. 5. The method according to claim 3, wherein when the number of the intermittently energized solar cell strings is one, intermittent energization of the solar cell strings excluded from the intermittent energization for a predetermined time is performed to detect a power generation enabled state. 3. The method for controlling snow melting according to item 1.