Photovoltaic inverter, photovoltaic inverter system and control method

Abstract

The present invention discloses a photovoltaic inverter, a photovoltaic inverter system, and a control method. The photovoltaic inverter includes a DC-DC conversion unit, a DC-LINK capacitor group, and a DC-AC conversion unit for sequential connection. The photovoltaic inverter also has a PV input terminal for connecting a photovoltaic string. The photovoltaic inverter also includes a string detection device for detecting whether the connected photovoltaic string is reversely connected. The string detection device includes: a current detection unit, which is used to detect the current at the PV input terminal and output a detection signal; a comparator unit, which is used to compare the voltage value of the detection signal with a reference voltage and output a signal indicating that the string is reversely connected when a set condition is met; and a power storage unit, which is used to power the current detection unit and the comparator unit; the photovoltaic inverter includes: a first charging unit, which is used to charge the power storage unit. The photovoltaic inverter can accurately detect the reverse connection of the PV string when it is not connected to the grid power supply and all the strings are reversely connected.

Description

Technical Field

[0001] The present invention belongs to the field of photovoltaic inverters and relates to a photovoltaic inverter, a photovoltaic inverter system and a control method. Background Art

[0002] As the core device that converts the direct current (DC) power provided by solar modules into alternating current (AC) power for civilian or industrial use, photovoltaic inverters are becoming increasingly important in the field of new energy. In recent years, with the plans for carbon peak and carbon neutrality, green energy has experienced explosive growth. The installed capacity of photovoltaic module power generation systems has been increasing, and they have become the main force of green energy. Since photovoltaic panels and inverters often encounter the problem of reverse connection of photovoltaic panel strings (hereinafter referred to as "PV strings") during construction and installation, how to efficiently and quickly identify reverse-connected strings and issue alarms to guide installers to make timely connection adjustments and maintenance is of great practical significance. However, current PV string reverse connection detection technology uses current sensors to collect string input current to determine whether it is reverse connected. It cannot accurately detect reverse connection when all PV strings are reverse connected and not connected to the grid power supply. Summary of the Invention

[0003] In response to the above technical problems, an object of the present invention is to provide a photovoltaic inverter and a photovoltaic inverter system that can accurately detect the reverse connection of PV strings when the grid power supply is not connected and all strings are reversely connected.

[0004] Another object of the present invention is to provide a control method for a photovoltaic inverter that can accurately detect the reverse connection of PV strings when the inverter is not connected to the grid power supply and all strings are reversely connected.

[0005] The present invention adopts the following technical solutions:

[0006] A photovoltaic inverter comprises a DC-DC converter unit, a DC-LINK capacitor bank, and a DC-AC converter unit connected in sequence. The photovoltaic inverter further comprises a PV input terminal for connecting a photovoltaic string. The photovoltaic inverter further comprises a string detection device for detecting whether the connected photovoltaic string is reversely connected. The string detection device is connected between the PV input terminal and the DC-DC converter unit. The string detection device comprises:

[0007] a current detection unit, configured to detect the current at the PV input terminal and output a detection signal;

[0008] a comparator unit, whose input end is connected to the output end of the current detection unit and is used to compare the voltage value of the detection signal with a reference voltage, and when a set condition is met, the comparator unit outputs a signal indicating reverse connection of the string; and

[0009] a power storage unit, connected to the current detection unit and the comparator unit respectively to supply power to the current detection unit and the comparator unit;

[0010] The photovoltaic inverter comprises:

[0011] A first charging unit is used to charge the power supply energy storage unit, wherein the input end of the first charging unit is connected to the DC-LINK capacitor group, and the output end is connected to the power supply energy storage unit.

[0012] Preferably, the string detection device further includes a second charging unit for charging the power storage unit, wherein the input end of the second charging unit is connected to the AC side of the DC-AC conversion unit, and the output end is connected to the power storage unit.

[0013] Preferably, the photovoltaic inverter further includes a control unit, and the output end of the comparator unit is connected to the control unit.

[0014] Preferably, the string detection device further includes an alarm unit, which is connected to the output of the comparator unit, and the power storage unit is connected to the alarm unit to supply power. The introduction of the alarm unit greatly facilitates installation and maintenance, and has important display significance.

[0015] Preferably, the alarm unit includes a status indicator light.

[0016] Preferably, the non-inverting input terminal of the comparator unit is connected to the reference voltage, and the inverting input terminal is connected to the output terminal of the current detection unit.

[0017] Preferably, the photovoltaic inverter includes multiple groups of PV input terminals and multiple string detection devices, each group of PV input terminals is used to connect to one photovoltaic string, each group of PV input terminals is respectively connected to a corresponding string detection device, and the output end of the first charging unit is respectively connected to the power storage unit of each of the string detection devices.

[0018] Preferably, the setting condition is: the voltage value of the detection signal is less than the reference voltage.

[0019] Preferably, the power storage unit is a supercapacitor.

[0020] The present invention also adopts the following technical solutions:

[0021] A photovoltaic inverter system includes a photovoltaic string and a photovoltaic inverter. The photovoltaic inverter adopts the photovoltaic inverter described above. The output end of the photovoltaic string is directly connected to the PV input end of the photovoltaic inverter.

[0022] The present invention also adopts the following technical solutions:

[0023] A control method for a photovoltaic inverter, wherein the photovoltaic inverter is the photovoltaic inverter described above, and the control method comprises the following steps:

[0024] In a maintenance or repair condition, and with the first charging unit not working, if the voltage value of the detection signal is less than the reference voltage, the comparator unit outputs a signal indicating reverse connection of the strings;

[0025] In a maintenance or repair condition, and with the first charging unit operating, if the voltage value of the detection signal is less than the reference voltage, the comparator unit outputs a signal indicating reverse connection of the strings;

[0026] Under the operating condition that the photovoltaic inverter is not yet connected to the grid and the second charging unit is not working, if the voltage value of the detection signal is less than the reference voltage, the comparator unit outputs a signal indicating that the string is reversely connected;

[0027] When the photovoltaic inverter is connected to the grid, the second charging unit operates, and if the voltage value of the detection signal is less than the reference voltage, the comparator unit outputs a signal indicating reverse connection of the strings.

[0028] Preferably, the signal indicating reverse connection of the strings output by the comparator unit is sent to the control unit of the photovoltaic inverter, or is sent to the alarm unit of the string detection device to enable the alarm unit to issue an alarm.

[0029] The present invention adopts the above solution and has the following advantages compared with the prior art:

[0030] A photovoltaic inverter, photovoltaic inverter system, and control method of the present invention integrate a string detection device into the photovoltaic inverter, and the string detection unit includes a power storage unit capable of powering it. This can realize the function of intelligently detecting string reverse connection when all operating conditions or all PV strings are reversed, effectively solving the difficulty of reverse connection of photovoltaic strings in actual installation applications, and can be achieved without connecting to the power grid, effectively ensuring the convenience and safety of installation and maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 is a circuit diagram of a photovoltaic inverter and a photovoltaic inverter system according to an embodiment;

[0033] Figure 2 This is the circuit diagram of the string detection device.

[0034] in,

[0035] 1. PV string; 2. String detection device; 3. DC-DC conversion unit; 4. DC-LINK capacitor group; 5. DC-AC conversion unit; 6. First charging unit; 7. Second charging unit; 8. Control unit; 9. Power grid; 10. PV inverter; 11. Current detection unit; 12. Comparator unit; 13. Power storage unit; 14. Alarm unit. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention are described in detail below with reference to 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. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0037] like Figure 1 As shown, this embodiment provides a photovoltaic inverter 10, comprising a string detection device 2, a DC-DC conversion unit 3, a DC-LINK capacitor group 4, and a DC-AC conversion unit 5 connected in sequence. The input end of the string detection device 2 is connected to the PV input terminals PV+ and PV- to detect whether the connected photovoltaic string is reversely connected. There are multiple groups of PV input terminals PV+ and PV-, and there are correspondingly multiple string detection devices 2. Each group of PV input terminals PV+ and PV- is used to connect to a photovoltaic string 1, and the photovoltaic string 1 is grounded. Each group of PV input terminals PV+ and PV- is respectively connected to a corresponding string detection device 2. The output end of the string detection device 2 is connected to the DC-DC conversion unit 3, and the electric energy output by the PV input terminals PV+ and PV- is connected to the DC-DC conversion unit 3 via the string detection device 2. The electric energy of the DC-DC conversion unit 3 can power the DC-LINK capacitor group 4.

[0038] The photovoltaic inverter 10 also includes a first charging unit 6, a second charging unit 7, and a control unit 8. The first charging unit 6 is used to charge the power storage unit 13. The input of the first charging unit 6 is connected to the DC-LINK capacitor bank 4, and the output is connected to the power storage unit 13. The output of the first charging unit 6 is also connected to the DC-AC conversion unit 5 to provide power to the DC-AC conversion unit 5. The first charging unit 6 specifically includes a switching power supply DC-SPS. The second charging unit 7 is also used to charge the power storage unit 13. The input of the second charging unit 7 is connected to the AC side of the DC-AC conversion unit 5. The second charging unit 7 specifically includes a switching power supply AC-SPS. The first charging unit 6 and the output of each string detection device 2 are respectively connected to the control unit 8. The DC-DC conversion unit 3 and the DC-AC conversion unit 5 are respectively connected to the control unit 8 for signal transmission. The first charging unit 6 and the second charging unit 7 can both provide power to the control unit 8.

[0039] like Figure 2 As shown, each string detection device 2 includes: a current detection unit 11, which is used to detect the current of the PV input terminals PV+ and PV- and output a detection signal. The output Vout of the current detection unit 11 is connected to the control unit 8 for detecting the string current and determining abnormalities; a comparator unit 12, whose input terminal is connected to the output terminal of the current detection unit 11 and is used to compare the voltage value of the detection signal with the reference voltage. When the voltage value of the detection signal is less than the reference voltage, the comparator unit 12 outputs a signal indicating reverse connection of the string. Specifically in this embodiment, the non-inverting input terminal of the comparator unit 12 is connected to the reference voltage, and the inverting input terminal is connected to the current. The output end of the detection unit 11 is connected; the power storage unit 13 is connected to the current detection unit 11 and the comparator unit 12 respectively to supply power to the current detection unit 11 and the comparator unit 12. Specifically, in this embodiment, the power storage unit 13 is a supercapacitor. The output end of the first charging unit 6 is respectively connected to the power storage unit 13 of each string detection device 2, and the output end of the second charging unit 7 is connected to the power storage unit 13; the alarm unit 14 is connected to the output end of the comparator unit 12. The alarm unit 14 includes a status indicator light. The status indicator light can receive an enable signal from the comparator output and then issue an alarm, that is, the indicator light is on. The photovoltaic inverter 10 also includes a voltage input terminal Vcc, which is connected to the power storage unit 13, the current detection unit 11, and the alarm unit 14 respectively to supply power to the power storage unit 13, the current detection unit 11, and the alarm unit 14. The first charging unit 6 and the second charging unit 7 can both supply power to the string detection device 2.

[0040] This embodiment also adopts the following technical solutions:

[0041] like Figure 1As shown in the figure, a photovoltaic inverter system includes a photovoltaic string 1 and a photovoltaic inverter. The photovoltaic inverter adopts the photovoltaic inverter 10 as described above. The output end of the photovoltaic string is directly connected to the PV input terminals PV+ and PV- of the photovoltaic inverter 10. There are multiple groups of PV input terminals PV+ and PV-, and correspondingly, there are also multiple string detection devices 2. Each group of PV input terminals PV+ and PV- is used to connect a photovoltaic string. Each group of PV input terminals PV+ and PV- is respectively connected to a corresponding string detection device 2, and each group of PV input terminals PV+ and PV- is grounded respectively. The AC side of the DC-AC conversion unit 5 is connected to the power grid 9. The DC-LINK capacitor bank 4 can convert direct current into alternating current through the DC-AC conversion unit 5 and connect it to the power grid 9, and the electric energy of the power grid 9 can be synchronously supplied to the second charging unit 7.

[0042] The following technical solutions are also adopted in this embodiment:

[0043] A control method for a photovoltaic inverter is implemented based on the photovoltaic inverter. The photovoltaic inverter is the photovoltaic inverter 10 as described above. The control method includes the following steps:

[0044] When some of the photovoltaic strings 1 are reversely connected, usually in the maintenance or repair working condition, and the DC-SPS unit does not work (the voltage of the non-reversely connected string is lower than the working voltage of the DC-SPS unit), the string detection device 2 is powered by the power storage unit 13. The output signal Vout of the current detection unit 11 is compared with the reference voltage Vref through the comparator unit 12. If Vout < Vref, the comparator unit 12 outputs a signal indicating that the string is reversely connected, and the comparator unit will output an enabling signal to enable the alarm unit 14 connected to it to give an alarm (such as status light indication);

[0045] When some of the photovoltaic strings 1 are reversely connected, usually in the maintenance or repair working condition, and the DC-SPS unit works (the voltage of the non-reversely connected string is higher than the working voltage of the DC-SPS unit), the string detection device 2 is powered by the DC-SPS unit. The output signal Vout of the current detection unit 11 is compared with the reference voltage Vref through the comparator unit 12. If Vout < Vref, the comparator unit 12 outputs a signal indicating that the string is reversely connected, and the comparator unit 12 will output an enabling signal to enable the alarm unit 14 connected to it to give an alarm (such as status light indication), and the control unit 8 will also detect the abnormal information of the string current and send the string reverse connection information to the inverter upper computer monitoring, etc.;

[0046] When all the photovoltaic strings 1 are reversely connected, it is usually in the working condition where the photovoltaic inverter 10 is not connected to the grid, and the AC-SPS unit does not work (no connection between the inverter and the grid or no AC-SPS unit). The string detection device 2 is powered by the power storage unit 13. The output signal Vout of the current detection unit 11 is compared with the reference voltage Vref through the comparator unit 12. If Vout < Vref, the comparator unit 12 outputs a signal indicating that the string is reversely connected, and the comparator will output an enable signal to enable the alarm unit 14 connected thereto to give an alarm (such as status light indication).

[0047] When all the photovoltaic strings 1 are reversely connected, it is usually in the working condition where the photovoltaic inverter 10 is connected to the grid, and the AC-SPS unit works (the inverter is connected to the grid). The string detection device 2 is powered by the AC-SPS unit. The output signal Vout of the current detection unit 11 is compared with the reference voltage Vref through the comparator unit 12. If Vout < Vref, the comparator unit 12 outputs a signal indicating that the string is reversely connected, and the comparator will output an enable signal to enable the alarm unit 14 connected thereto to give an alarm (such as status light indication). The control unit 8 will also detect the abnormal string current information and send the string reverse connection information to the upper computer monitoring of the inverter, etc.

[0048] This embodiment provides a photovoltaic inverter and photovoltaic inverter system, including a string detection device 2 connected between PV input terminals PV+ and PV- and a DC-DC converter unit 3. The string detection device 2 is integrated into a photovoltaic inverter 10. A current detection unit 11 in the string detection device 2 outputs a signal that is compared with a reference voltage. Based on the comparison result, a comparator unit 12 can output a signal indicating string reverse connection to an alarm unit 14 to issue an alarm. This allows reverse connection detection of photovoltaic strings 1 under all inverter operating conditions (maintenance or repair phase, installation phase). Furthermore, in addition to reverse connection of some photovoltaic strings 1, the photovoltaic inverter 10 can also intelligently detect reverse connection of all photovoltaic strings 1. Furthermore, because the current detection unit 11 can be powered by a power storage unit 13, the photovoltaic inverter system can intelligently identify and detect reverse connection of photovoltaic strings 1 regardless of whether the inverter is connected to the grid or whether the first charging unit 6 and the second charging unit 7 are operating normally, and issue an alarm by illuminating an indicator light. This photovoltaic inverter system not only effectively solves the problem of how to detect whether the photovoltaic string 1 is reversely connected, but also can quickly and accurately intelligently identify and issue an alarm even when the grid power supply is not connected and all strings are reversely connected, greatly ensuring the convenience and effectiveness of application. Through the introduction of the alarm unit 14, the convenience and safety of installation and maintenance are effectively guaranteed, which has important display significance. The control method of a photovoltaic inverter provided in this embodiment can realize the function of intelligently detecting the reverse connection of the strings when all operating conditions are met or all photovoltaic strings 1 are reversely connected, effectively solving the difficulty of reverse connection of the photovoltaic strings 1 in actual installation applications. Detection can be achieved without connecting to the grid, effectively ensuring the convenience and safety of installation and maintenance.

[0049] The above embodiment is intended only to illustrate the technical concepts and features of the present invention and is a preferred embodiment. Its purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. It is not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A photovoltaic inverter comprising a DC-DC converter unit, a DC-LINK capacitor bank, and a DC-AC converter unit connected in sequence, wherein the photovoltaic inverter further comprises a PV input terminal for connecting a photovoltaic string, wherein: The photovoltaic inverter further includes a string detection device for detecting whether the connected photovoltaic strings are reversely connected. The string detection device is connected between the PV input terminal and the DC-DC conversion unit. The string detection device includes: a current detection unit, configured to detect the current at the PV input terminal and output a detection signal; a comparator unit, whose input end is connected to the output end of the current detection unit and is used to compare the voltage value of the detection signal with a reference voltage, and when a set condition is met, the comparator unit outputs a signal indicating reverse connection of the string; and a power storage unit, connected to the current detection unit and the comparator unit respectively to supply power to the current detection unit and the comparator unit; The photovoltaic inverter comprises: A first charging unit is used to charge the power supply energy storage unit, wherein the input end of the first charging unit is connected to the DC-LINK capacitor group, and the output end is connected to the power supply energy storage unit.

2. The photovoltaic inverter according to claim 1, characterized in that: The string detection device further includes a second charging unit for charging the power storage unit, wherein an input end of the second charging unit is connected to the AC side of the DC-AC conversion unit, and an output end of the second charging unit is connected to the power storage unit.

3. The photovoltaic inverter according to claim 1, characterized in that: The photovoltaic inverter further includes a control unit, and the output end of the comparator unit is connected to the control unit.

4. The photovoltaic inverter according to claim 1, characterized in that: The string detection device further includes an alarm unit, which is connected to the output end of the comparator unit. The power storage unit is connected to the alarm unit to supply power to the alarm unit.

5. The photovoltaic inverter according to claim 1, characterized in that: The non-inverting input terminal of the comparator unit is connected to the reference voltage, and the inverting input terminal is connected to the output terminal of the current detection unit.

6. The photovoltaic inverter according to claim 1, characterized in that: The photovoltaic inverter includes multiple groups of PV input terminals and multiple string detection devices. Each group of PV input terminals is used to connect to one photovoltaic string. Each group of PV input terminals is respectively connected to a corresponding string detection device. The output end of the first charging unit is respectively connected to the power storage unit of each string detection device.

7. The photovoltaic inverter according to claim 1, characterized in that: The setting condition is that the voltage value of the detection signal is less than the reference voltage.

8. The photovoltaic inverter according to claim 1, characterized in that: The power storage unit is a supercapacitor.

9. A photovoltaic inverter system, comprising a photovoltaic string and a photovoltaic inverter, characterized in that: The photovoltaic inverter is the photovoltaic inverter according to any one of claims 1 to 8, and the output end of the photovoltaic string is directly connected to the PV input end of the photovoltaic inverter.

10. A control method for a photovoltaic inverter, characterized in that: The photovoltaic inverter is the photovoltaic inverter according to any one of claims 1 to 8, and the control method comprises the following steps: In a maintenance or repair condition, and with the first charging unit not working, if the voltage value of the detection signal is less than the reference voltage, the comparator unit outputs a signal indicating reverse connection of the strings; In a maintenance or repair condition, and with the first charging unit operating, if the voltage value of the detection signal is less than the reference voltage, the comparator unit outputs a signal indicating reverse connection of the strings; Under the operating condition that the photovoltaic inverter is not yet connected to the grid and the second charging unit is not working, if the voltage value of the detection signal is less than the reference voltage, the comparator unit outputs a signal indicating that the string is reversely connected; When the photovoltaic inverter is connected to the grid, the second charging unit operates, and if the voltage value of the detection signal is less than the reference voltage, the comparator unit outputs a signal indicating reverse connection of the strings.

11. The control method according to claim 10, characterized in that: The signal indicating reverse connection of the strings output by the comparator unit is sent to the control unit of the photovoltaic inverter, or is sent to the alarm unit of the string detection device to enable the alarm unit to issue an alarm.

Images