A conversion device, system and method for photovoltaic power station

Abstract

The present invention discloses a conversion device, system and method for a photovoltaic power station, which can convert a relatively high photovoltaic open-circuit voltage for use by an inverter. A conversion device for a photovoltaic power station, the conversion device having an input positive terminal and an input negative terminal for connecting the output of a photovoltaic panel, and an output positive terminal and an output negative terminal for connecting the input of a photovoltaic inverter; the conversion device comprises a first voltage-dividing resistor and a second voltage-dividing resistor connected in series between the input positive terminal and the input negative terminal; the output positive terminal is connected to the middle point of the first voltage-dividing resistor and the second voltage-dividing resistor; the output negative terminal is connected to the input negative terminal; the conversion device also comprises a first switch connected in parallel to both ends of the first voltage-dividing resistor and a second switch connected in series between the second voltage-dividing resistor and the input negative terminal.

Description

Technical Field

[0001] The present invention belongs to the field of photovoltaic power generation, and in particular relates to a conversion device, system and method for a photovoltaic power station. Background Art

[0002] As the core device that converts the direct current provided by the solar module into alternating current for civil or industrial use, the photovoltaic inverter is becoming increasingly important in the field of new energy. At present, the MPPT input voltage range of the photovoltaic inverter has been designed. However, in some special cases, the maximum output open-circuit voltage of the photovoltaic panel connected by the user is high, while the MPPT working voltage is low. If the current photovoltaic inverter is used, when the open-circuit voltage is high and the inverter is not working, the voltage is large and exceeds the inverter input voltage range, which may permanently damage the inverter. Therefore, the inverter cannot be used in this condition. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a conversion device, system and method for a photovoltaic power station, which can convert a relatively high photovoltaic open-circuit voltage for use by an inverter.

[0004] The first aspect of the present invention provides a conversion device for a photovoltaic power station, the conversion device having an input positive terminal and an input negative terminal for connecting the output of a photovoltaic panel, and an output positive terminal and an output negative terminal for connecting the input of a photovoltaic inverter; the conversion device includes a first voltage-dividing resistor and a second voltage-dividing resistor connected in series between the input positive terminal and the input negative terminal; the output positive terminal is connected to the middle point of the first voltage-dividing resistor and the second voltage-dividing resistor; the output negative terminal is connected to the input negative terminal; the conversion device also includes a first switch connected in parallel to both ends of the first voltage-dividing resistor and a second switch connected in series between the second voltage-dividing resistor and the input negative terminal.

[0005] Preferably, the conversion device has a first working mode and a second working mode. When the conversion device is in the first working mode, the first switch is closed and the second switch is open; when the conversion device is in the second working mode, the first switch is open and the second switch is turned on.

[0006] Preferably, the conversion device further comprises a DC / DC converter for converting the voltage input from the photovoltaic panel into a low voltage for driving the first switch and the second switch.

[0007] More preferably, the conversion device further comprises an overvoltage protector, and the overvoltage protector is used to stop the output of the DC / DC converter when the voltage input from the photovoltaic panel is higher than a set value.

[0008] More preferably, the first switch is a normally open relay, and the second switch is a normally closed relay.

[0009] More preferably, the DC / DC converter is connected in series between the positive input terminal and the negative input terminal.

[0010] A second aspect of the present invention provides a conversion system for a photovoltaic power station, comprising a photovoltaic panel and a photovoltaic relay, the conversion system also comprising a conversion device as described above, the conversion device being connected between the photovoltaic panel and the photovoltaic relay, wherein the positive input terminal and the negative input terminal of the conversion device are electrically connected to the positive output terminal and the negative output terminal of the photovoltaic panel, respectively, and the positive output terminal and the negative output terminal of the conversion device are electrically connected to the positive input terminal and the negative input terminal of the photovoltaic inverter, respectively.

[0011] Preferably, the photovoltaic inverter comprises a housing and components arranged in the housing, and the conversion device is located outside the housing.

[0012] The third aspect of the present invention provides a conversion method for the conversion device as described above, the method comprising the following steps: when the voltage input by the photovoltaic panel is lower than or equal to a set value, closing the first switch and opening the second switch; when the voltage input by the photovoltaic panel is higher than the set value, opening the first switch and closing the second switch.

[0013] Preferably, the first switch is a normally open relay, and the second switch is a normally closed relay. The contacts of the first switch and the second switch are driven to act by a DC / DC converter, and the output voltage of the DC / DC converter is controlled by an overvoltage protector. When the voltage input by the photovoltaic panel is lower than or equal to a set value, the DC / DC converter converts the voltage into a low voltage to drive the normally open contact of the first switch to close and the normally closed contact of the second switch to open, so that the conversion device is in a first working mode; when the voltage input by the photovoltaic panel is higher than the set value, the overvoltage protector is activated to stop the input of the DC / DC converter, the normally open contact of the first switch is opened, and the normally closed contact of the second switch is closed, so that the conversion device is in a second working mode.

[0014] The present invention adopts the above solution, which has the following advantages compared with the prior art:

[0015] The conversion device of the present invention is a device that can convert a relatively high photovoltaic open-circuit output voltage for use by a photovoltaic inverter. The device is connected between a photovoltaic panel and a photovoltaic inverter, and serves as an intermediate bridge connecting the photovoltaic panel and the photovoltaic inverter, without changing the system architecture of the current photovoltaic power station. The conversion device has few components, low cost, low loss, and high efficiency. It is placed outside the photovoltaic inverter, does not need to change the system architecture of the photovoltaic power station, and is directly connected between the photovoltaic panel and the photovoltaic inverter. It is particularly suitable for a photovoltaic inverter system in which the open-circuit voltage of the photovoltaic panel is relatively high and the applicable voltage range of the photovoltaic inverter is relatively low. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0017] Figure 1 is a structural schematic diagram of a conversion system according to an embodiment of the present invention;

[0018] Figure 2 4 is a circuit diagram of a conversion device according to an embodiment of the present invention.

[0019] in:

[0020] 1. Photovoltaic panel; 2. Conversion device; 3. Photovoltaic inverter; 4. Power grid;

[0021] 21. Positive input terminal; 22. Negative input terminal; 23. First voltage-dividing resistor; 24. Second voltage-dividing resistor; 25. First switch; 26. Second switch; 27. DC / DC converter; 28. Overvoltage protector; 29. ​​Positive output terminal; 30. Negative output terminal. DETAILED DESCRIPTION

[0022] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0023] This embodiment provides a conversion device for a photovoltaic power station. This embodiment also provides a conversion system for a photovoltaic power station, which includes the above-mentioned conversion device. This embodiment further provides a conversion method using the above-mentioned conversion device.

[0024] like Figure 1 As shown, the conversion system for a photovoltaic power station includes a photovoltaic panel 1, the above-mentioned conversion device 2 and a photovoltaic inverter 3. The photovoltaic panel 1 is used to convert the energy of sunlight into electrical energy and output direct current. The conversion device 2 is connected between the photovoltaic panel 1 and the photovoltaic inverter 3, and is used to reduce the voltage when the open-circuit voltage output by the photovoltaic panel 1 is too high, and then supply it to the photovoltaic inverter 3 to convert it into alternating current, and then feed it to the power grid 4. When the open-circuit voltage output by the photovoltaic panel 1 is less than the set value, the direct current output by the photovoltaic panel 1 is directly supplied to the photovoltaic inverter through the conversion device 2 without voltage reduction. The "set value" mentioned in this article can be the maximum value of the MPPT input voltage allowed by the photovoltaic inverter.

[0025] The above-mentioned conversion device is specifically as follows Figure 2 As shown. The conversion device has an input positive terminal PV+21 and an input negative terminal PV-21 for connecting the output of the photovoltaic panel, and a first voltage-dividing resistor R1 23 and a second voltage-dividing resistor R2 24 are connected in series between the input positive terminal PV+21 and the input negative terminal PV-21. The conversion device also has an output positive terminal PV1+29 and an output negative terminal PV1-30 for connecting the input of the photovoltaic inverter, the output positive terminal PV1+29 is connected to the middle point of the first voltage-dividing resistor R1 23 and the second voltage-dividing resistor R2 24, and the output negative terminal PV1-30 is connected to the input negative terminal PV-21. The conversion device also includes a first switch 25 and a second switch 26, the first switch 25 is connected in parallel to the first voltage-dividing resistor R1 23, and the second switch 26 is connected in series between the second voltage-dividing resistor R2 24 and the input negative terminal PV-21. The conversion device has a first working mode and a second working mode. When the conversion device is in the first working mode, the first switch 25 is closed and the second switch 26 is open. When the conversion device is in the second working mode, the first switch 25 is turned off and the second switch 26 is turned on.

[0026] The conversion device also includes a DC / DC converter 27 for converting the voltage input by the photovoltaic panel into a low voltage to drive the first switch 25 and the second switch 26. Specifically, the first switch 25 is a normally open relay having a normally open contact NO; the second switch 26 is a normally closed relay having a normally closed contact NC. The DC / DC converter 27 is connected in series between the positive input terminal PV+21 and the negative input terminal PV-21, and its output terminal is electrically connected to the first switch 25 and the second switch 26. The DC / DC converter 27 converts the voltage input by the photovoltaic panel into a low voltage, and drives the normally open contact NO of the first switch 25 to close and the normally closed contact NC of the second switch 26 to open through the low voltage.

[0027] The conversion device further includes an overvoltage protector 28 , which is used to stop the DC / DC converter 27 from outputting when the voltage input from the photovoltaic panel is higher than a set value. The overvoltage protector 28 is electrically connected to the DC / DC converter 27 .

[0028] like Figure 1 As shown, in a photovoltaic power generation system, the positive and negative poles of the output end of the photovoltaic panel 1 are directly electrically connected to the positive pole PV+21 and the negative pole PV-21 of the input end of the above-mentioned conversion device 2, and the positive pole PV1+29 and the negative pole PV1-30 of the output end of the conversion device 2 are directly electrically connected to the positive pole and the negative pole of the input end of the photovoltaic inverter 3. It should also be noted that the conversion device 2 is located outside the housing of the photovoltaic inverter 3. Specifically, the photovoltaic inverter 3 includes a housing, and the electronic components of the photovoltaic inverter 3 are arranged in the housing, while the above-mentioned conversion device 2 is located outside the housing. In other words, the conversion device of this embodiment is placed outside the photovoltaic inverter and is directly connected between the photovoltaic panel and the photovoltaic inverter. There is no need to change the system architecture of the built power station, and it can be easily applied to scenarios where the maximum output open-circuit voltage of some photovoltaic panels is greater than the current photovoltaic inverter input MPPT voltage.

[0029] For example, the maximum MPPT input voltage of a single-phase photovoltaic inverter is currently 600V, while in some cases the maximum open-circuit voltage output by a photovoltaic panel is 800V. If a photovoltaic inverter with a maximum input voltage of 600V is directly connected to a photovoltaic panel with a maximum open-circuit voltage of 800V, the photovoltaic inverter is likely to be permanently damaged. The conversion device of this embodiment is connected between the photovoltaic panel and the photovoltaic inverter to solve this problem well, so that the 600V photovoltaic inverter in the current market can be applied to the photovoltaic panel system with a maximum open-circuit voltage of 800V.

[0030] When the open circuit voltage of the photovoltaic panel is between 0 and 600V, the DC / DC converter 27 works normally, the output voltage closes the normally open contact of the first switch 25, the normally closed contact of the second switch 26 is disconnected, the first voltage-dividing resistor R1 23 is short-circuited, and the second voltage-dividing resistor R2 24 loop is disconnected (that is, the conversion device is in the first working mode), and the photovoltaic panel output voltage is directly connected to the input end of the photovoltaic inverter through the first switch 25, so that the photovoltaic inverter can work normally. That is, the conversion device of this embodiment does not affect the working mode when the open circuit voltage of the photovoltaic panel is low.

[0031] When the open-circuit voltage of the photovoltaic panel is between 600V and 800V, the overvoltage protector 28 performs a protective action, the DC / DC converter 27 stops outputting, the output voltage is 0, the relay coils of the first switch 25 and the second switch 26 cannot obtain a driving voltage, the normally open contact of the first switch 25 is disconnected, the normally closed contact of the second switch 26 is closed, the first voltage-dividing resistor R1 23 and the second voltage-dividing resistor R2 24 are connected to the loop for voltage division (i.e., the conversion device is in the second working mode), and the higher open-circuit voltage of the photovoltaic panel is divided and output to the photovoltaic inverter. The voltage will be lower than 600V, which meets the input voltage range of the photovoltaic inverter. After the inverter starts working, the MPPT voltage will drop. When the voltage drops below 600V, the overvoltage protector 28 is released, the DC / DC converter 27 resumes normal operation, and the output voltage closes the normally open contact of the first switch 25 and disconnects the normally closed contact of the second switch 26. The first voltage-dividing resistor R1 23 is short-circuited, and the second voltage-dividing resistor R2 24 loop is disconnected (that is, the conversion device is restored to the first working mode). The output voltage of the photovoltaic panel is directly connected to the input end of the photovoltaic inverter through the first switch 25, so that the photovoltaic inverter (3) can work normally.

[0032] This embodiment also provides a conversion method of the conversion device as described above, the method comprising the following steps: when the voltage input by the photovoltaic panel is lower than or equal to the set value, closing the first switch 25 and opening the second switch 26; when the voltage input by the photovoltaic panel is higher than the set value, opening the first switch 25 and closing the second switch 26.

[0033] The conversion method further includes the following steps: driving the contacts of the first switch 25 and the second switch 26 to operate through the DC / DC converter 27, and controlling the output voltage of the DC / DC converter 27 through the overvoltage protector 28; when the voltage input by the photovoltaic panel is lower than or equal to the set value, the DC / DC converter 27 converts the voltage into a low voltage to drive the normally open contact of the first switch 25 to close and the normally closed contact of the second switch 26 to open, so that the conversion device is in the first working mode; when the voltage input by the photovoltaic panel is higher than the set value, the overvoltage protector 28 is activated to stop the input of the DC / DC converter 27, the normally open contact of the first switch 25 is opened, and the normally closed contact of the second switch 26 is closed, so that the conversion device is in the second working mode.

[0034] The conversion device of this embodiment is a device that can convert a higher photovoltaic open-circuit output voltage for use by a photovoltaic inverter. This device is connected between a photovoltaic panel and a photovoltaic inverter as an intermediate bridge connecting the photovoltaic panel and the photovoltaic inverter, without changing the system architecture of the current photovoltaic power station. When the photovoltaic panel open-circuit voltage is higher than the MPPT input voltage range of the photovoltaic inverter, this device will reduce the high voltage and output it for use by the photovoltaic inverter, so that the photovoltaic inverter can work normally. After the photovoltaic inverter works, the panel output voltage will drop. When the panel output voltage drops to the MPPT input voltage range of the photovoltaic inverter, this device switches to another working mode, and will not continue to reduce the low voltage output by the panel, but use the panel output voltage for the inverter to work; when the photovoltaic panel open-circuit output voltage is within the MPPT input voltage range of the photovoltaic inverter, this device is equivalent to a short-circuit state, does not change the voltage output by the photovoltaic panel to the photovoltaic inverter, does not change the normal working voltage of the inverter, and has no effect on it.

[0035] The above-mentioned conversion device has few components, low cost, small loss and high efficiency. It is placed outside the photovoltaic inverter and does not need to change the system architecture of the photovoltaic power station. It is directly connected between the photovoltaic panel and the photovoltaic inverter. It is particularly suitable for photovoltaic inverter systems with high open-circuit voltage of the photovoltaic panel and low applicable voltage range of the inverter.

[0036] The above embodiment is only for illustrating the technical concept and features of the present invention, and is a preferred embodiment. Its purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A conversion system for a photovoltaic power station, comprising a photovoltaic panel and a photovoltaic inverter, characterized in that: The conversion system also includes a conversion device, which is connected between the photovoltaic panel and the photovoltaic inverter, wherein the conversion device has an input positive terminal and an input negative terminal for connecting the output of the photovoltaic panel, and an output positive terminal and an output negative terminal for connecting the input of the photovoltaic inverter; the conversion device includes a first voltage-dividing resistor and a second voltage-dividing resistor connected in series between the input positive terminal and the input negative terminal; the output positive terminal is connected to the middle point of the first voltage-dividing resistor and the second voltage-dividing resistor; the output negative terminal is connected to the input negative terminal; the conversion device also includes a first switch connected in parallel to both ends of the first voltage-dividing resistor and a second switch connected in series between the second voltage-dividing resistor and the input negative terminal; The conversion device further includes a DC / DC converter for converting the voltage inputted from the photovoltaic panel into a low voltage for driving the first switch and the second switch; the conversion device further includes an overvoltage protector, which is used to stop the output of the DC / DC converter when the voltage inputted from the photovoltaic panel is higher than a set value; The positive input terminal and the negative input terminal of the conversion device are electrically connected to the positive output terminal and the negative output terminal of the photovoltaic panel, respectively, and the positive output terminal and the negative output terminal of the conversion device are electrically connected to the positive input terminal and the negative input terminal of the photovoltaic inverter, respectively; When the open-circuit voltage of the photovoltaic panel is greater than the MPPT input voltage range of the photovoltaic inverter, the first switch is disconnected, the second switch is closed, and the photovoltaic inverter operates normally; until the open-circuit voltage of the photovoltaic panel drops to within the MPPT input voltage range of the photovoltaic inverter, the conversion device is switched to another operating mode, the first switch is closed, and the second switch is disconnected; The contacts of the first switch and the second switch are driven to move by the DC / DC converter, and the output voltage of the DC / DC converter is controlled by the overvoltage protector; when the open-circuit voltage of the photovoltaic panel is lower than or equal to a set value, the DC / DC converter converts the voltage into a low voltage to drive the normally open contact of the first switch to close and the normally closed contact of the second switch to open; when the open-circuit voltage of the photovoltaic panel is higher than the set value, the overvoltage protector is activated to stop the input of the DC / DC converter, the normally open contact of the first switch is opened, and the normally closed contact of the second switch is closed, so that the conversion device is in the second working mode.

2. The conversion system according to claim 1, characterized in that: The photovoltaic inverter comprises a housing and components arranged in the housing, and the conversion device is located outside the housing.

3. The conversion system according to claim 1, characterized in that: The first switch is a normally open relay, and the second switch is a normally closed relay.

4. The conversion system according to claim 1, characterized in that: The DC / DC converter is connected in series between the positive input terminal and the negative input terminal.

5. A conversion method of a conversion system according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: when the voltage input by the photovoltaic panel is lower than or equal to a set value, closing the first switch and opening the second switch; when the voltage input by the photovoltaic panel is higher than the set value, opening the first switch and closing the second switch.

6. The conversion method according to claim 5, characterized in that: The first switch is a normally open relay, and the second switch is a normally closed relay. The contacts of the first switch and the second switch are driven to operate by a DC / DC converter, and the output voltage of the DC / DC converter is controlled by an overvoltage protector. When the voltage input by the photovoltaic panel is lower than or equal to a set value, the DC / DC converter converts the voltage into a low voltage to drive the normally open contact of the first switch to close and the normally closed contact of the second switch to open, so that the conversion device is in a first working mode; when the voltage input by the photovoltaic panel is higher than the set value, the overvoltage protector is activated to stop the input of the DC / DC converter, the normally open contact of the first switch is opened, and the normally closed contact of the second switch is closed, so that the conversion device is in a second working mode.

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