Photovoltaic power generation system

Abstract

The invention discloses a photovoltaic power generation system, and belongs to the technical field of power generation. The system comprises an inverter circuit, an alternating-current starting circuit and a control unit, the alternating-current starting circuit comprises an alternating-current starting switch, an isolation module and a charging module which are sequentially connected from a power grid side, and the control unit is connected with the inverter circuit and the alternating-current starting switch. The control unit is used for controlling the alternating-current starting switch to be closed and transmitting electric energy of a power grid through the isolation module when the direct-current voltage of the input end of the inverter circuit is lower than the sum of the power grid line voltage peak-to-peak value and a threshold value and an alternating-current starting instruction is received, and the charging module carries out current limiting and rectifying processing on alternating-current electric energy output by the isolation module. The direct-current bus capacitor is charged by alternating positive and negative half waves of alternating current; and the control unit is also used for controlling the alternating current starting switch to be switched off and starting the inverter circuit under the condition that the direct current bus capacitor is charged to the target voltage required by grid connection. The system can be safely and reliably started when no sunlight exists at night.

Description

Technical Field

[0001] This application belongs to the technical field of power generation, and particularly relates to a photovoltaic power generation system. Background Art

[0002] The combined use of photovoltaic and energy storage has become the mainstream trend in the new energy field. The photovoltaic system generates electricity during the day, and the energy storage system can store the excess electricity. Devices such as energy storage inverters and photovoltaic grid-connected inverters not only work during the day but also need to perform battery charging and discharging or power compensation at night to maintain a stable power supply.

[0003] Since there is no sunlight at night, the solar panels at the DC power supply end commonly used for starting cannot supply power to devices such as energy storage inverters and photovoltaic grid-connected inverters; powering on these devices through the energy storage battery may cause over-discharge of the battery and even damage.

[0004] How to start devices such as energy storage inverters and photovoltaic grid-connected inverters when there is no sunlight at night is one of the technical problems urgently to be solved in this field. Summary of the Invention

[0005] This application aims to solve at least one of the technical problems existing in the prior art. For this purpose, this application proposes a photovoltaic power generation system that can be started safely and reliably when there is no sunlight at night.

[0006] In a first aspect, this application provides a photovoltaic power generation system, including:

[0007] An inverter circuit, the output end of the inverter circuit is connected to the power grid, and a DC bus capacitor is provided at the input end of the inverter circuit;

[0008] An AC starting circuit, the AC starting circuit includes an AC starting switch, an isolation module, and a charging module connected in sequence from the power grid side. The AC starting switch is also connected to the power grid, and the charging module is also connected to the DC bus capacitor;

[0009] A control unit, the control unit is connected to the inverter circuit and the AC starting switch. The control unit is configured to control the AC starting switch to close when the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the power grid line voltage plus a threshold and an AC starting instruction is received, transmit the electric energy of the power grid through the isolation module, the charging module performs current limiting and rectification processing on the AC electric energy output by the isolation module, and charges the DC bus capacitor through the positive and negative half-waves of the alternating current. The isolation module isolates the power grid and the DC bus capacitor;

[0010] The control unit is further configured to control the AC starting switch to open and start the inverter circuit when the DC bus capacitor is charged to the target voltage required for grid connection, so that the photovoltaic power generation system operates in grid-connected mode.

[0011] According to the photovoltaic power generation system of the present application, an AC starting circuit is formed by sequentially connecting an AC starting switch, an isolation module, and a charging module from the grid side. When the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the grid line voltage plus a threshold and an AC starting instruction is received, the control unit controls the AC starting switch to close, conducts the AC starting circuit to charge the DC bus capacitor, and can safely and reliably start the photovoltaic power generation system at night without sunlight, which helps the subsequent execution of system grid connection, reactive power compensation, fault restart and other operations.

[0012] According to an embodiment of the present application, it further includes:

[0013] A grid connection switch device, which is arranged between the output end of the inverter circuit and the grid.

[0014] According to an embodiment of the present application, the grid connection switch device includes a first grid connection switch and a second grid connection switch connected in sequence. The first grid connection switch is close to the grid, and the second grid connection switch is close to the inverter circuit.

[0015] According to an embodiment of the present application, the AC starting switch is connected to the connection point between the first grid connection switch and the second grid connection switch. The control unit is also connected to the grid connection switch device. The control unit is further configured to control the AC starting switch and the first grid connection switch to close when the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the grid line voltage plus a threshold and the AC starting instruction is received, transmit the electric energy of the grid through the isolation module, the charging module performs current limiting and rectification processing on the AC electric energy output by the isolation module, charges the DC bus capacitor through the alternating positive and negative half waves of the alternating current, and the isolation module isolates the grid and the DC bus capacitor;

[0016] Alternatively, the AC starting switch is connected to the connection point between the grid and the first grid connection switch. The control unit is also connected to the grid connection switch device. The control unit is further configured to control the AC starting switch to close when the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the grid line voltage plus a threshold and the AC starting instruction is received, transmit the electric energy of the grid through the isolation module, the charging module performs current limiting and rectification processing on the AC electric energy output by the isolation module, charges the DC bus capacitor through the alternating positive and negative half waves of the alternating current, and the isolation module isolates the grid and the DC bus capacitor.

[0017] According to an embodiment of the present application, the closed first grid-connection switch is located on the phase line connected to the AC starting circuit.

[0018] According to an embodiment of the present application, the control unit is configured to disconnect the AC starting switch and the first grid-connection switch and control the startup of the inverter circuit when the residual current detection and insulation impedance detection of the inverter circuit are passed and the voltage of the DC bus capacitor reaches the target voltage required for grid connection.

[0019] According to an embodiment of the present application, the control unit is further configured to control the second grid-connection switch and the first grid-connection switch to close when the inverter circuit has been started and the output voltage of the inverter circuit and the grid-side voltage of the power grid meet the grid-connection conditions, so that the photovoltaic power generation system operates in grid connection.

[0020] According to an embodiment of the present application, the control unit is configured to control the second grid-connection switch and the first grid-connection switch to close when the grid-connection switch device passes the self-check.

[0021] According to an embodiment of the present application, the control unit is further configured to output a startup failure warning message when the residual current detection of the inverter circuit, the insulation impedance detection of the inverter circuit, or the self-check of the grid-connection switch device fails.

[0022] According to an embodiment of the present application, it further includes:

[0023] An AC auxiliary power supply, the control unit is connected to the power grid through the AC auxiliary power supply, and the AC auxiliary power supply is configured to convert the AC electric energy of the power grid into DC electric energy to supply power to the control unit.

[0024] According to an embodiment of the present application, the DC bus capacitor includes a positive bus capacitor and a negative bus capacitor, and one end of the positive bus capacitor and one end of the negative bus capacitor are connected to the bus midpoint.

[0025] According to an embodiment of the present application, it further includes:

[0026] A voltage equalizing switch device, the voltage equalizing switch device includes a first voltage equalizing switch and a second voltage equalizing switch, a first end of the charging module is connected to the bus midpoint, a second end of the charging module is connected to the other end of the positive bus capacitor, a third end of the charging module is connected to the other end of the negative bus capacitor, the first voltage equalizing switch is arranged between the second end of the charging module and the other end of the positive bus capacitor, and the second voltage equalizing switch is arranged between the third end of the charging module and the other end of the negative bus capacitor;

[0027] The control unit is connected to the voltage equalizing switch device. The control unit is configured to, when the voltage difference between the positive bus capacitor and the negative bus capacitor is greater than a preset voltage threshold, based on the voltages of the positive bus capacitor and the negative bus capacitor, control one of the first voltage equalizing switch and the second voltage equalizing switch to open and the other to close;

[0028] Wherein, when the first voltage equalizing switch is closed and the second voltage equalizing switch is open, the charging module charges the positive bus capacitor; when the first voltage equalizing switch is open and the second voltage equalizing switch is closed, the charging module charges the negative bus capacitor.

[0029] According to an embodiment of the present application, the charging module includes a series-connected current-limiting resistor and a rectifying circuit. The current-limiting resistor is used to limit the charging current of the DC bus capacitor, and the rectifying circuit is used to charge the DC bus capacitor.

[0030] According to an embodiment of the present application, the control unit is further configured to, when the DC input voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the grid line voltage plus a threshold and an AC start command is received, output an auxiliary power source off command to control the AC start switch to close to charge the DC bus capacitor.

[0031] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, wherein:

[0033] Figure 1 is one of the schematic structural diagrams of the photovoltaic power generation system provided by the embodiment of the present application;

[0034] Figure 2 is another schematic structural diagram of the photovoltaic power generation system provided by the embodiment of the present application;

[0035] Figure 3 is Figure 2 the equivalent topology diagram of;

[0036] Figure 4 is one of the schematic structural diagrams of the photovoltaic power generation system provided by the embodiment of the present application;

[0037] Figure 5 is one of the schematic structural diagrams of the photovoltaic power generation system provided by the embodiment of the present application;

[0038] Figure 6 is Figure 5Equivalent topology diagram;

[0039] Figure 7 It is the fourth structural schematic diagram of the photovoltaic power generation system provided by the embodiment of the present application;

[0040] Figure 8 It is the fifth structural schematic diagram of the photovoltaic power generation system provided by the embodiment of the present application;

[0041] Figure 9 It is the sixth structural schematic diagram of the photovoltaic power generation system provided by the embodiment of the present application;

[0042] Figure 10 It is the process schematic diagram of the AC starting of the photovoltaic power generation system provided by the embodiment of the present application.

[0043] Reference numerals:

[0044] Inverter circuit 100, DC input port 101, battery pack unit 102, DC bus capacitor 200,

[0045] AC start switch 310, isolation module 320, current limiting resistor 331, rectifier circuit 332, voltage equalizing switch device 340,

[0046] First grid connection switch 410, second grid connection switch 420,

[0047] Control unit 510, AC auxiliary power supply 520, power grid 600. Detailed implementation manners

[0048] Next, the technical solutions in the embodiments of the present application will be clearly described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present application.

[0049] The terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects, rather than to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are usually of the same type, and the number of objects is not limited. For example, the first object can be one or multiple. In addition, "and / or" in the description and claims means at least one of the connected objects, and the character " / " generally means an "or" relationship between the associated objects before and after.

[0050] Next, the photovoltaic power generation system provided by the embodiment of the present application will be described in detail in conjunction with the accompanying drawings, through specific embodiments and their application scenarios.

[0051] As Figure 1 shown, the photovoltaic power generation system includes: an inverter circuit 100, an AC starting circuit, and a control unit 510.

[0052] Among them, the inverter circuit 100 can convert direct current into alternating current. The output end of the inverter circuit 100 is connected to the power grid 600, and a DC bus capacitor 200 is provided at the input end of the inverter circuit 100.

[0053] In this embodiment, the DC input port 101 of the inverter circuit 100 can be connected to devices such as solar panels. When there is sunlight during the day, the DC bus capacitor 200 can be charged through the DC input of the DC input port 101 to start the photovoltaic power generation system.

[0054] It can be understood that for a photovoltaic power generation system connected with an energy storage device, the battery pack unit 102 of the energy storage device can be arranged at the input end of the inverter circuit 100.

[0055] The AC starting circuit can use the alternating current of the power grid 600 to charge the DC bus capacitor 200 when there is no DC input at the DC input port 101, so as to realize the AC starting of the photovoltaic power generation system.

[0056] In this embodiment, the AC starting circuit includes an AC starting switch 310, an isolation module 320, and a charging module connected in sequence from the power grid 600 side. The AC starting switch 310 is also connected to the power grid 600, and the charging module is also connected to the DC bus capacitor 200.

[0057] Among them, the AC starting switch 310 can control the on-off of the power transmission between the power grid 600 and the DC bus capacitor 200.

[0058] It should be noted that when the isolation module 320 transmits electrical energy from the power grid 600 to the DC bus capacitor 200, it can also achieve electrical isolation between the power grid 600 and the DC bus capacitor 200, preventing electric leakage when the power grid 600 charges the DC bus capacitor 200.

[0059] In actual implementation, the isolation module 320 can be a device such as an isolation transformer that realizes electrical isolation while transmitting electrical energy.

[0060] The charging module rectifies, limits the current, etc. of the alternating current of the power grid 600 and converts it into direct current to charge the DC bus capacitor 200 and increase the voltage of the DC bus capacitor 200.

[0061] In some embodiments, the charging module includes a series-connected current-limiting resistor 331 and a rectifying circuit 332. The current-limiting resistor 331 is used to limit the charging current of the DC bus capacitor 200, and the rectifying circuit 332 is used to charge the DC bus capacitor 200.

[0062] Among them, the rectifying circuit 332 can convert the AC electrical energy provided by the power grid 600 into DC electrical energy to supply the DC bus capacitor 200 for charging and increase the voltage of the DC bus capacitor 200.

[0063] In actual implementation, the rectifying circuit 332 can be topological structures such as half-wave rectification, full-wave rectification, and bridge rectification.

[0064] It can be understood that the current-limiting resistor 331 is used to limit the charging current. By setting the current-limiting resistor 331 in both the positive and negative branches of the AC starting circuit, the magnetizing inrush current at the moment when the isolation module 320 is powered on can be suppressed, preventing the switches such as the AC starting switch 310 from sticking due to excessive current, and also preventing the circuit breaker on the AC side from tripping due to excessive magnetizing inrush current.

[0065] The control unit 510 is connected to the inverter circuit 100 and the AC starting switch 310. The control unit 510 is configured to control the AC starting switch 310 to close when the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the grid line voltage plus a threshold and an AC starting instruction is received, transmit the electrical energy of the power grid 600 through the isolation module 320, the charging module performs current limiting and rectifying processing on the AC electrical energy output by the isolation module 320, and charges the DC bus capacitor 200 through the positive and negative half-cycles of the alternating current. The isolation module 320 isolates the power grid 600 from the DC bus capacitor 200, and during the charging process, there will be no electric leakage in the power grid 600.

[0066] In this embodiment, the voltage at the input end of the inverter circuit 100 is detected. When the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the grid line voltage plus a threshold, it indicates that the DC input of the photovoltaic power generation system cannot supply power to the inverter circuit 100, that is, the photovoltaic power generation system may be in a situation without sunlight at night.

[0067] Among them, the peak-to-peak value of the grid line voltage refers to the difference between the maximum value of the positive half-cycle and the minimum value of the negative half-cycle of the grid line voltage of the power grid 600 in a complete cycle. When the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the grid line voltage plus a preset threshold (which can be a positive value), it indicates that there is no DC input to the inverter circuit 100, and the photovoltaic power generation system may be in a situation without sunlight at night.

[0068] When the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the grid line voltage plus a threshold value, and the control unit 510 receives an AC start instruction, the control unit 510 controls the AC start switch 310 to close, conducts the AC starting circuit, the isolation module 320 outputs alternating current, which is converted into direct current of a certain magnitude through the current-limiting resistor 331 and the rectifier circuit 332 of the charging module, and is output to the DC bus capacitor 200 to charge the DC bus capacitor 200 through the positive and negative half-waves of the alternating current.

[0069] It can be understood that during the charging process of the DC bus capacitor 200, the voltage of the DC bus capacitor 200 gradually increases. The voltage of the DC bus capacitor 200 is detected in real time to determine whether the starting conditions of the inverter circuit 100 are met.

[0070] In this embodiment, the control unit 510 is further configured to control the AC start switch 310 to disconnect when the DC bus capacitor 200 is charged to the target voltage required for grid connection, and start the inverter circuit 100 to enable the photovoltaic power generation system to operate in grid connection.

[0071] Among them, the target voltage required for grid connection is the voltage required for the photovoltaic power generation system to be connected to the grid, and can be set according to the voltage of the grid 600.

[0072] In the related art, due to no sunlight at night, the commonly used DC power supply end solar panels of the starting machine cannot supply power to equipment such as energy storage inverters and photovoltaic grid-connected inverters; using the energy storage battery to supply power to start these devices may cause over-discharge of the battery and even damage.

[0073] In the embodiment of the present application, the photovoltaic power generation system is provided with an AC starting circuit. The AC starting circuit includes an AC start switch 310, an isolation module 320, and a charging module connected in sequence from the grid 600 side. When the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the grid line voltage plus a threshold value and the control unit 510 receives an AC start instruction, the control unit 510 controls the AC start switch 310 to close, conducts the AC starting circuit to charge the DC bus capacitor 200, and can use alternating current to charge the DC bus capacitor 200 at night without sunlight. The inverter circuit 100 of the photovoltaic power generation system can be normally started to complete actions such as grid connection, reactive power compensation, and fault restart.

[0074] It should be noted that when the AC starting circuit is turned on, a charging loop is formed from the power grid 600 to the DC bus capacitor 200. The AC starting circuit is provided with an isolation module 320 that can achieve electrical isolation, which can effectively prevent leakage when the power grid 600 charges the DC bus capacitor 200. Compared with the related technology where a charging loop is formed from the grid side to the bus capacitor and then back to the grid side, the embodiment of the present application can form a complete charging loop without returning to the grid side again, which can effectively reduce the leakage probability during the charging process of the power grid 600 to the DC bus capacitor 200, and can safely and reliably start the photovoltaic power generation system at night when there is no sunlight.

[0075] According to the photovoltaic power generation system provided by the embodiment of the present application, an AC starting circuit is formed by sequentially connecting an AC starting switch 310, an isolation module 320, and a charging module from the power grid 600 side. When the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the power grid line voltage plus a threshold and an AC starting instruction is received, the control unit 510 controls the AC starting switch 310 to close, turning on the AC starting circuit to charge the DC bus capacitor 200, which can safely and reliably start the photovoltaic power generation system at night when there is no sunlight, and helps to execute subsequent system grid connection, reactive power compensation, fault restart and other operations.

[0076] In some embodiments, the photovoltaic power generation system may further include an AC auxiliary power supply 520.

[0077] As Figure 1 shown, the control unit 510 is connected to the power grid 600 through the AC auxiliary power supply 520, and the AC auxiliary power supply 520 is used to convert the AC electric energy of the power grid 600 into DC electric energy to supply power to the control unit 510.

[0078] In this embodiment, the AC auxiliary power supply 520 converts the AC electric energy of the power grid 600 into DC electric energy, outputs the DC electric energy to the control unit 510 to supply power to the control unit 510, and ensures the stable operation of the control unit 510 for the scenario of no sunlight at night.

[0079] In some embodiments, the photovoltaic power generation system may further include a grid connection switch device, which is disposed between the output end of the inverter circuit 100 and the power grid 600.

[0080] It can be understood that the grid connection switch device is a key component connecting the inverter circuit 100 and the power grid 600, which can control the power transmission between the inverter circuit 100 and the power grid 600, safely and stably connect the electric energy output by the inverter circuit 100 to the power grid 600 at an appropriate time to realize the grid-connected operation of the photovoltaic power generation system, and can also disconnect the connection with the power grid 600 when the power grid 600 has an abnormality or a fault to protect the equipment of the photovoltaic power generation system.

[0081] As shown Figure 5 in the figure, the AC starting circuit includes an AC starting switch 310, an isolation module 320, and a charging module that are sequentially connected on the grid 600 side. When the control unit 510 controls the AC starting switch 310 to close, electric energy is transmitted from the grid 600 to the DC bus capacitor 200 through the AC starting switch 310, the isolation module 320, and the charging module.

[0082] In this embodiment, when the AC starting circuit is turned on, a charging loop from the grid 600 to the DC bus capacitor 200 is formed. The loop for charging the DC bus capacitor 200 may not pass through the grid-connected switch device, which can improve the safety and reliability of the start-up of the photovoltaic power generation system.

[0083] In some embodiments, the grid-connected switch device includes a first grid-connected switch 410 and a second grid-connected switch 420 that are sequentially connected. The first grid-connected switch 410 is close to the grid 600, and the second grid-connected switch 420 is close to the inverter circuit 100.

[0084] In this embodiment, the first grid-connected switch 410 of the grid-connected switch device that is close to the grid 600 and the second grid-connected switch 420 that is close to the inverter circuit 100 are in series. When the inverter circuit 100 starts and meets the grid-connection conditions, the control unit 510 controls both the first grid-connected switch 410 and the second grid-connected switch 420 to close, realizing the grid-connected operation of the photovoltaic power generation system.

[0085] In some embodiments, the AC starting switch 310 is connected to the connection point between the grid 600 and the first grid-connected switch 410. The control unit 510 is also connected to the grid-connected switch device. The control unit 510 is further configured to control the AC starting switch 310 to close when the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the grid line voltage plus a threshold and an AC starting instruction is received, transmit the electric energy of the grid 600 through the isolation module 320, the charging module performs current limiting and rectification processing on the AC electric energy output by the isolation module 320, charges the DC bus capacitor 200 through the alternating positive and negative half-waves of the alternating current, and the isolation module 320 isolates the grid 600 and the DC bus capacitor 200, so that there is no electric leakage in the grid 600 during the charging process.

[0086] In this embodiment, the AC starting switch 310 is connected to the power grid 600, and there is no grid connection switch between the AC starting switch 310 and the power grid 600. The control unit 510 is configured to control the closing of the AC starting switch 310 when the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the power grid line voltage plus a threshold value and an AC starting instruction is received, transmit the electric energy of the power grid 600 through the isolation module 320, the charging module performs current limiting and rectification processing on the AC electric energy output by the isolation module 320, and charges the DC bus capacitor 200 through the alternating positive and negative half waves of the alternating current. The isolation module 320 isolates the power grid 600 from the DC bus capacitor 200, so that there is no electric leakage in the power grid 600 during the charging process.

[0087] For example, as Figure 4 shown, for a three-phase system of A, B, and C, the second grid connection switch 420 close to the inverter circuit 100 includes K A1 , K B1 , K C1 , the first grid connection switch 410 close to the power grid 600 includes K A2 , K B2 , K C2 , the phase lines connected to the AC starting circuit are B and C, and there is no grid connection switch between the AC starting switch 310 and the power grid 600.

[0088] In this embodiment, after receiving the AC starting instruction, the control unit 510 controls the closing of S1, S2, S3, and S4 of the AC starting switch 310, conducts the AC starting circuit, and charges the DC bus capacitor 200.

[0089] In some embodiments, the AC starting switch 310 is connected to the connection point between the first grid connection switch 410 and the second grid connection switch 420. The control unit 510 is also connected to the grid connection switch device. The control unit 510 is further configured to control the closing of the AC starting switch 310 and the first grid connection switch 410 when the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the power grid line voltage plus a threshold value and an AC starting instruction is received, transmit the electric energy of the power grid 600 through the isolation module 320, and the charging module performs current limiting and rectification processing on the AC electric energy output by the isolation module 320, and charges the DC bus capacitor 200 through the alternating positive and negative half waves of the alternating current.

[0090] As Figure 2 shown, the AC starting switch 310 is connected to the connection point between the first grid connection switch 410 and the second grid connection switch 420, controls the closing of the first grid connection switch 410 close to the power grid 600, and controls the closing of the AC starting switch 310, conducts the AC starting circuit, and charges the DC bus capacitor 200 through the isolation module 320 and the charging module.

[0091] As Figure 3As shown, to charge the DC bus capacitor 200, the AC electric energy output by the power grid 600 sequentially passes through the first grid-connection switch 410, the AC start switch 310, the isolation module 320, the current-limiting resistor 331, and the rectifier circuit 332, and is supplied to the DC bus capacitor 200.

[0092] In this embodiment, the charging circuit of the DC bus capacitor 200 does not return to the power grid 600 through the second grid-connection switch 420, which can reduce the probability of leakage and switch adhesion during the charging process.

[0093] It can be understood that the AC start switch 310 is connected to the connection point between the first grid-connection switch 410 and the second grid-connection switch 420, and controls the actions of the first grid-connection switch 410 and the AC start switch 310 to turn on the AC starting circuit, which can reduce the probability of mis-turning on the AC starting circuit when the first grid-connection switch 410 or the AC start switch 310 is stuck.

[0094] In some embodiments, the closed first grid-connection switch 410 is located on the phase line connected to the AC starting circuit.

[0095] In actual implementation, the number of the first grid-connection switches 410 can be one or more, and the number of the second grid-connection switches 420 can also be one or more.

[0096] When controlling the conduction of the AC starting circuit, the closed first grid-connection switch 410 is located on the phase line connected to the AC starting circuit, that is, the first grid-connection switch 410 on the phase line not connected to the AC starting circuit can remain open.

[0097] For example, as Figure 2 shown, for the A, B, C three-phase system, the second grid-connection switch 420 close to the inverter circuit 100 includes K A1 、K B1 、K C1 , the first grid-connection switch 410 close to the power grid 600 includes K A2 、K B2 、K C2 , and the phase lines connected to the AC starting circuit are B and C.

[0098] In this embodiment, after receiving the AC start command, the control unit 510 controls the K B2 、K C2 of the first grid-connection switch 410 to close, and the control unit 510 controls the S1, S2, S3, S4 of the AC start switch 310 to close, turning on the AC starting circuit to charge the DC bus capacitor 200.

[0099] In some embodiments, the control unit 510 is configured to disconnect the AC starting switch 310 and the first grid-connection switch 410 when the residual current detection and insulation impedance detection of the inverter circuit 100 are passed and the voltage of the DC bus capacitor 200 reaches the target voltage required for grid connection, and control the startup of the inverter circuit 100.

[0100] In this embodiment, the AC starting circuit is turned on to charge the DC bus capacitor 200. During the rising process of the voltage of the DC bus capacitor 200, the photovoltaic power generation system performs residual current detection and insulation impedance detection, and determines whether the voltage of the DC bus capacitor 200 reaches the threshold voltage (the target voltage required for grid connection) required for grid connection. When the residual current detection and insulation impedance detection are passed and the bus voltage reaches the threshold voltage required for grid connection, the control unit 510 controls the disconnection of the AC starting switch 310 and the first grid-connection switch 410 to disconnect the AC starting circuit and control the startup of the inverter circuit 100.

[0101] Among them, the residual current detection (RCD) determines whether there is a leakage situation by detecting the difference between the current flowing into and out of the circuit, and the insulation impedance detection (ISO) is used to evaluate the insulation performance between the photovoltaic power generation system and the ground. By measuring the insulation resistance between the internal circuit of the system and the ground, it is judged whether there is a risk of insulation degradation or leakage.

[0102] It can be understood that performing residual current detection and insulation impedance detection before starting the inverter circuit 100 can improve the safety and reliability of the operation of the photovoltaic power generation system.

[0103] In some embodiments, the control unit 510 is further configured to control the second grid-connection switch 420 and the first grid-connection switch 410 to close when the inverter circuit 100 has been started and the voltage at the output end of the inverter circuit 100 and the grid-side voltage of the power grid 600 meet the grid-connection conditions, so that the photovoltaic power generation system operates in parallel with the grid.

[0104] It can be understood that after the inverter circuit 100 is started, the control unit 510 controls the output of the inverter circuit 100 so that the voltage at the output end of the inverter circuit 100 follows the grid-side voltage of the power grid 600 to reach the grid-connection conditions, and controls the second grid-connection switch 420 and the first grid-connection switch 410 to close to realize the connection between the inverter circuit 100 and the power grid 600.

[0105] In actual implementation, the grid-connection conditions may include that the voltage at the output end of the inverter circuit 100 is synchronized with the grid-side voltage of the power grid 600 in amplitude, frequency and phase, the frequency output by the inverter circuit 100 is the same as the frequency of the power grid 600, and the voltage waveform output by the inverter circuit 100 is close to the sine wave waveform of the power grid 600 and other conditions.

[0106] In some embodiments, the control unit 510 is configured to control the second grid-connection switch 420 and the first grid-connection switch 410 to close when the grid-connection switch device passes the self-check.

[0107] In this embodiment, before controlling the second grid-connection switch 420 and the first grid-connection switch 410 to close, the second grid-connection switch 420 and the first grid-connection switch 410 of the grid-connection switch device are self-checked. When the second grid-connection switch 420 and the first grid-connection switch 410 pass the self-check, the second grid-connection switch 420 and the first grid-connection switch 410 are then controlled to close.

[0108] In actual implementation, the self-check of the grid-connection switch device may include detections of aspects such as switch position, switch adhesion, and switch electrical performance. When the grid-connection switch device passes the self-check, the second grid-connection switch 420 and the first grid-connection switch 410 are then controlled to close to achieve grid connection, which can improve the safety and reliability of the grid-connected operation of the photovoltaic power generation system.

[0109] It should be noted that during the AC startup process of the photovoltaic power generation system, detections such as the residual current detection of the inverter circuit 100, the insulation impedance detection of the inverter circuit 100, or the self-check of the grid-connection switch device can be performed. When the residual current detection of the inverter circuit 100, the insulation impedance detection of the inverter circuit 100, or the self-check of the grid-connection switch device all pass, the AC startup of the photovoltaic power generation system can be completed to achieve the grid-connected operation of the system.

[0110] In some embodiments, the control unit 510 is further configured to output a startup failure warning message when the residual current detection of the inverter circuit 100, the insulation impedance detection of the inverter circuit 100, or the self-check of the grid-connection switch device fails.

[0111] During the AC startup process, if at least one of the residual current detection of the inverter circuit 100, the insulation impedance detection of the inverter circuit 100, and the self-check of the grid-connection switch device fails, the AC startup fails, and a startup failure warning message is output to prompt the staff that the current AC startup has failed. Information prompting the staff to repair the relevant lines can also be output.

[0112] In some embodiments, the DC bus capacitor 200 includes a positive bus capacitor and a negative bus capacitor. One end of the positive bus capacitor and one end of the negative bus capacitor are connected to the bus midpoint.

[0113] In this embodiment, the DC bus is divided into a positive bus and a negative bus. The DC bus capacitor 200 includes a positive bus capacitor connected to the positive bus and a negative bus capacitor connected to the negative bus. The connection point of the positive bus capacitor and the negative bus capacitor is the bus midpoint.

[0114] For example, as Figure 2As shown, the DC bus capacitor 200 includes a positive bus capacitor C1 and a negative bus capacitor C2, and C1 and C2 are connected to the midpoint of the bus.

[0115] In some embodiments, the photovoltaic power generation system may further include a voltage equalizing switch device 340.

[0116] In this embodiment, the voltage equalizing switch device 340 includes a first voltage equalizing switch and a second voltage equalizing switch. The first end of the charging module is connected to the midpoint of the bus, the second end of the charging module is connected to the other end of the positive bus capacitor, the third end of the charging module is connected to the other end of the negative bus capacitor, the first voltage equalizing switch is disposed between the second end of the charging module and the other end of the positive bus capacitor, and the second voltage equalizing switch is disposed between the third end of the charging module and the other end of the negative bus capacitor.

[0117] The charging module branches out into two branches. The branch where the second end is located is connected to the positive bus capacitor, the branch where the third end is located is connected to the negative bus capacitor, and the first end of the charging module is connected to the midpoint of the bus, forming a circuit that can charge the positive bus capacitor and the negative bus capacitor separately.

[0118] Among them, when the first voltage equalizing switch is closed and the second voltage equalizing switch is open, the charging module charges the positive bus capacitor; when the first voltage equalizing switch is open and the second voltage equalizing switch is closed, the charging module charges the negative bus capacitor.

[0119] The control unit 510 is connected to the voltage equalizing switch device 340. The control unit 510 is configured to, when the voltage difference between the positive bus capacitor and the negative bus capacitor is greater than a preset voltage threshold, based on the voltage of the positive bus capacitor and the voltage of the negative bus capacitor, control one of the first voltage equalizing switch and the second voltage equalizing switch to open and the other to close.

[0120] In this embodiment, during the charging process of the DC bus capacitor 200, the voltages of the positive bus capacitor and the negative bus capacitor are monitored in real time. When the voltage difference (i.e., voltage difference) between the positive bus capacitor and the negative bus capacitor is greater than the preset voltage threshold, it indicates that the positive and negative bus voltages are uneven. The control unit 510 controls the conduction and cutoff of the first voltage equalizing switch and the second voltage equalizing switch in the voltage equalizing switch device 340 to charge the positive bus capacitor or the negative bus capacitor separately, reducing the voltage difference between the positive bus capacitor and the negative bus capacitor, so that the positive and negative buses are voltage-equalized.

[0121] It should be noted that the preset voltage threshold is a preset critical value of the voltage difference. The preset voltage threshold can be a positive value greater than 0. The voltage difference between the positive bus capacitor and the negative bus capacitor is greater than the preset voltage threshold, that is, the absolute value of the voltage difference between the positive bus capacitor and the negative bus capacitor is greater than the preset voltage threshold.

[0122] In actual implementation, when it is determined that the voltage difference between the positive bus capacitor and the negative bus capacitor is greater than the preset voltage threshold, based on the voltage magnitudes of the positive bus capacitor and the negative bus capacitor, the capacitor with the lower voltage is determined, and the control unit 510 controls the conduction and cutoff of the first voltage equalizing switch and the second voltage equalizing switch to charge the capacitor with the lower voltage alone, reducing the voltage difference between the two capacitors and achieving equal voltage for the positive and negative buses.

[0123] For example, as Figure 2 shown, the DC bus capacitor 200 includes a positive bus capacitor C1 and a negative bus capacitor C2. C1 and C2 are connected to the midpoint of the bus. The charging module includes a current limiting resistor 331 and a rectifying module. The current limiting resistor 331 includes R1 and R2, and the rectifying module includes D1 and D2. One end of R2 is connected to the midpoint of the bus (i.e., the first end of the charging module is connected to the midpoint of the bus). One end of R1 is connected to C2 through D1 and is also connected to C1 through D2.

[0124] In this embodiment, the voltage equalizing switch device 340 includes S7 and S8. S8 disposed between D2 and C1 serves as the first voltage equalizing switch, and S7 disposed between D1 and C2 serves as the second voltage equalizing switch. When S8 is closed and S7 is open, the charging module charges C1. When S8 is open and S7 is closed, the charging module charges C2.

[0125] When the voltage difference between C1 and C2 is greater than the preset voltage threshold and the voltage of C1 is greater than the voltage of C2, the control unit 510 controls S8 to open and S7 to close, and the charging module charges C2 to reduce the voltage difference between C1 and C2.

[0126] When the voltage difference between C1 and C2 is greater than the preset voltage threshold and the voltage of C1 is less than the voltage of C2, the control unit 510 controls S8 to close and S7 to open, and the charging module charges C1 to reduce the voltage difference between C1 and C2.

[0127] In this embodiment, by monitoring the voltages of the positive bus capacitor and the negative bus capacitor and controlling the on-off of the first voltage equalizing switch and the second voltage equalizing switch, charging the positive bus capacitor or the negative bus capacitor alone is achieved, enabling the positive and negative buses to maintain equal voltage during the charging process of the DC bus capacitor 200 and improving the safety of the charging process.

[0128] In some embodiments, the control unit 510 is further configured to output an auxiliary source off command and control the AC start switch 310 to close to charge the DC bus capacitor 200 when the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the grid line voltage plus a threshold and an AC start command is received.

[0129] In this embodiment, during the AC startup process of the photovoltaic power generation system, an auxiliary power source shutdown instruction is output. The auxiliary power source shutdown instruction is used to instruct the shutdown of the auxiliary power source in the photovoltaic power generation system and other systems connected thereto, so as to minimize the power consumption of the photovoltaic power generation system, improve the charging rate of the DC bus capacitor 200, and help improve the AC startup efficiency of the photovoltaic power generation system.

[0130] For example, when the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the grid line voltage plus a threshold and an AC startup instruction is received, the control unit 510 outputs an auxiliary power source shutdown instruction. Through the auxiliary power source shutdown instruction, the DC auxiliary power source of the photovoltaic power generation system itself is shut down, and the auxiliary power source shutdown instruction is sent to the energy storage unit connected to the photovoltaic power generation system, so that the energy storage unit shuts down its auxiliary power source, greatly improving the charging rate of the DC bus capacitor 200.

[0131] To enable those skilled in the art to more comprehensively understand the technical solutions of this application, the following will specifically describe this application in combination with specific embodiments, fully demonstrating the implementation process of this application in actual application scenarios.

[0132] As Figure 1 shown, the photovoltaic power generation system includes devices such as a DC bus capacitor 200, an inverter circuit 100, a first grid connection switch 410, a second grid connection switch 420, an AC startup switch 310, an isolation module 320, a charging module, an AC auxiliary power source 520, and a control unit 510.

[0133] Among them, the DC bus capacitor 200 may include a positive bus capacitor and a negative bus capacitor, and the connection point of the positive bus capacitor and the negative bus capacitor is the bus midpoint.

[0134] The control unit 510 is connected to the power grid 600 through the AC auxiliary power source 520. The AC auxiliary power source 520 is used to convert the alternating current of the power grid 600 into direct current to supply power to the control unit 510.

[0135] As Figure 2 shown, for the A, B, C three-phase system, the second grid connection switch 420 close to the inverter circuit 100 includes K A1 , K B1 , K C1 , and the first grid connection switch 410 close to the power grid 600 includes K A2 , K B2 , K C2 , and the phase lines connected to the AC startup circuit are B and C.

[0136] The AC startup switch 310 includes S1, S2, S3, S4, the current limiting resistor 331 includes R1 and R2, the rectification module includes D1 and D2, and the isolation module 320 is an isolation transformer T1.

[0137] The DC bus capacitor 200 includes a positive bus capacitor C1 and a negative bus capacitor C2. C1 and C2 are connected to the midpoint of the bus. One end of R2 is connected to the midpoint of the bus. One end of R1 is connected to C2 through D1 and is also connected to C1 through D2.

[0138] In this embodiment, after the control unit 510 receives an AC start instruction, it controls the K B2 and K C2 of the first grid-connection switch 410 to close, and controls the S1, S2, S3, and S4 of the AC start switch 310 to close, conducting the AC starting circuit. The alternating current passes through the isolation transformer T1, the diode D1, and the diode D2 to charge C1 and C2.

[0139] The photovoltaic power generation system can also be provided with a voltage equalization switch device 340. S8 provided between D2 and C1 is used as the first voltage equalization switch, and S7 provided between D1 and C2 is used as the second voltage equalization switch. When S8 is closed and S7 is open, the charging module charges C1. When S8 is open and S7 is closed, the charging module charges C2.

[0140] During the process of charging the bus, when it is detected that the positive and negative bus voltages are uneven, the conduction and cutoff of S7 and S8 are controlled to equalize the positive and negative bus voltages.

[0141] When the voltage difference between C1 and C2 is greater than the preset voltage threshold and the voltage of C1 is greater than the voltage of C2, the control unit 510 controls S8 to open and S7 to close, and the charging module charges C2. When the voltage difference between C1 and C2 is greater than the preset voltage threshold and the voltage of C1 is less than the voltage of C2, the control unit 510 controls S8 to close and S7 to open, and the charging module charges C1.

[0142] It can be understood that when the voltage difference between C1 and C2 is less than or equal to the preset voltage threshold, it indicates that there is no situation of uneven positive and negative bus voltages. S7 and S8 are both closed to charge C1 and C2 simultaneously.

[0143] Figure 2 Shown is a specific topological structure of the inverter circuit 100 in the embodiment of the present application. Each phase bridge arm in the inverter circuit 100 is composed of 4 controllable switch tubes. Each phase is connected to the second grid-connection switch 420 through an LC filter circuit. The inverter circuit 100 of the photovoltaic power generation system includes, but is not limited to, topological structures such as T-type, I-type, ANPC-type, and HERIC-type.

[0144] It can be understood that the rectifier circuit 332 is used to convert alternating current into direct current. As Figure 2 shown, the rectifier circuit 332 can include a half-wave rectification topological structure of two diodes D1 and D2. The rectifier circuit 332 can also be a full-wave rectification topological structure as Figure 5 shown. As Figure 6As shown, the alternating current passes through the isolation transformer T1, the current-limiting resistors 331 (R1 and R2), and the full-wave rectification topology to charge the capacitors C1 and C2.

[0145] The photovoltaic power generation system according to the embodiment of the present application can also be applied to single-phase systems, including but not limited to single-phase systems such as HERIC.

[0146] As Figure 7 shown, the second grid connection switch 420 near the inverter circuit 100 includes K A1 , K B1 , and the first grid connection switch 410 near the power grid 600 includes K A2 , K B2 . The AC start switch 310 includes S1 and S2, the current-limiting resistor 331 includes R1 and R2, the rectification module includes D1 and D2, and the isolation module 320 is the isolation transformer T1.

[0147] D1 and D2 can form a half-wave rectification topology. S7 is set between D1 and C2, and S8 is set between D2 and C1. When the bus voltage is uneven, the control unit 510 can charge C1 or C2 separately by controlling the on / off of S7 and S8.

[0148] Figure 7 As shown, the inverter circuit 100 is composed of 4 controllable switch tubes. As Figure 8 shown, the inverter circuit 100 can also include more than 4 controllable switch tubes. The inverter circuit 100 of the photovoltaic power generation system includes but is not limited to topologies such as T-type, I-type, ANPC-type, and HERIC-type.

[0149] As Figure 7 and Figure 8 shown, after receiving the AC start instruction, the control unit 510 controls the S1 and S2 of the AC start switch 310 to close, and then the AC start-up circuit can be turned on. The alternating current passes through the isolation transformer T1, the diode D1, and the diode D2 to charge C1 and C2.

[0150] Figure 7 and Figure 8 shown, the rectifier circuit 332 is a half-wave rectification topology formed by D1 and D2. As Figure 9 shown, the rectifier circuit 332 can also be a full-wave rectification topology.

[0151] Next, taking the photovoltaic power generation system including an inverter as an example, the AC start-up process of the photovoltaic power generation system will be specifically introduced.

[0152] As Figure 10 shown, in the absence of DC voltage (which may be the case of no sunlight at night), that is, without DC input, the upper computer issues an AC start instruction.

[0153] The control unit 510 detects the bus voltage. When the bus voltage is less than the reference voltage for grid connection (i.e., the target voltage required for grid connection), it turns off the DC auxiliary power source of the inverter itself, and at the same time makes the energy storage unit connected to the inverter turn off the auxiliary power source, so as to minimize the power consumption.

[0154] The control unit 510 controls the AC start switch 310 to close, conducts the AC starting circuit, transmits the electric energy of the power grid 600 through the isolation module 320, and the charging module performs current limiting and rectification processing on the AC electric energy output by the isolation module 320, and charges the DC bus capacitor 200 through the alternating positive and negative half waves of the alternating current.

[0155] During the process of charging the DC bus capacitor 200, the bus voltage rises. The bus voltage is detected in real time, and at the same time, residual current detection (RCD) and insulation impedance detection (ISO) are performed.

[0156] It should be noted that when performing ISO detection, the AC start switch 310 can be disconnected. After passing the ISO detection, the AC start switch 310 is closed to compensate for the voltage drop during the ISO detection process.

[0157] When the bus voltage is greater than or equal to the reference voltage required for grid connection, the inverter circuit 100 is started, the AC start switch 310 is disconnected, and self-checks of the first grid connection switch 410 and the second grid connection switch 420 are performed. After passing the self-check of the grid connection switch, the control unit controls the first grid connection switch 410 and the second grid connection switch 420 to close, and the inverter is connected to the grid for operation.

[0158] During the AC starting process, if the RCD detection, ISO detection, or self-check of the grid connection switch fails, the AC starting will fail, and the corresponding alarm information will be displayed.

[0159] In this embodiment, an AC starting circuit is formed by sequentially connecting an AC start switch 310, an isolation module 320, and a charging module from the power grid 600 side. The control unit 510 controls the on-off of each switch in the system, conducts the AC starting circuit to charge the DC bus capacitor 200, and can safely and reliably start the photovoltaic power generation system at night without sunlight.

[0160] The embodiments of the present application have been described above in conjunction with the accompanying drawings. However, the present application is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present application, those of ordinary skill in the art can also make many forms without departing from the purpose of the present application and the scope protected by the claims, and all of them fall within the protection scope of the present application.

[0161] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0162] Although the embodiments of this application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and purposes of this application, and the scope of this application is defined by the claims and their equivalents.

Claims

1. A photovoltaic power generation system, characterized in that: include: An inverter circuit, wherein the output end of the inverter circuit is connected to the power grid, and the input end of the inverter circuit is provided with a DC bus capacitor; an AC starting circuit, the AC starting circuit comprising an AC starting switch, an isolation module and a charging module connected in sequence from the grid side, the AC starting switch is also connected to the grid, and the charging module is also connected to the DC bus capacitor; A control unit, the control unit is connected to the inverter circuit and the AC start switch, the control unit is used to control the AC start switch to close when the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the grid line voltage plus a threshold value and an AC start instruction is received, and the power of the grid is transmitted through the isolation module, the charging module performs current limiting and rectification processing on the AC power output by the isolation module, and charges the DC bus capacitor through alternating positive and negative half-waves of the AC power, and the isolation module isolates the grid from the DC bus capacitor; The control unit is also used to control the AC starting switch to be disconnected and start the inverter circuit when the DC bus capacitor is charged to the target voltage required for grid connection, so that the photovoltaic power generation system can be connected to the grid.

2. The photovoltaic power generation system according to claim 1, characterized in that: Also includes: A grid-connected switch device is arranged between the output end of the inverter circuit and the power grid.

3. The photovoltaic power generation system according to claim 2, characterized in that: The grid-connected switch device comprises a first grid-connected switch and a second grid-connected switch connected in sequence, wherein the first grid-connected switch is close to the power grid, and the second grid-connected switch is close to the inverter circuit.

4. The photovoltaic power generation system according to claim 3, characterized in that: The AC start switch is connected to the connection point between the first grid-connected switch and the second grid-connected switch, the control unit is also connected to the grid-connected switch device, and the control unit is also used to control the AC start switch and the first grid-connected switch to be closed when the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the grid line voltage plus a threshold value and the AC start instruction is received, and the power of the grid is transmitted through the isolation module, the charging module performs current limiting and rectification processing on the AC power output by the isolation module, and charges the DC bus capacitor through alternating positive and negative half-waves of the AC power, and the isolation module isolates the grid from the DC bus capacitor; Alternatively, the AC starting switch is connected to a connection point between the power grid and the first grid-connected switch, the control unit is also connected to the grid-connected switch device, and the control unit is also used to control the AC starting switch to close when the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the power grid line voltage plus a threshold and the AC starting instruction is received, and the electric energy of the power grid is transmitted through the isolation module. The charging module limits and rectifies the AC electric energy output by the isolation module, and charges the DC bus capacitor by alternating positive and negative half-waves of the AC power. The isolation module isolates the power grid and the DC bus capacitor.

5. The photovoltaic power generation system according to claim 4, characterized in that: The closed first grid-connected switch is located on the phase line connected to the AC starting circuit.

6. The photovoltaic power generation system according to claim 4, characterized in that: The control unit is used to disconnect the AC starting switch and the first grid-connected switch to control the startup of the inverter circuit when the residual current detection and the insulation impedance detection of the inverter circuit are passed and the voltage of the DC bus capacitor reaches the target voltage required for the grid connection.

7. The photovoltaic power generation system according to claim 3, characterized in that: The control unit is also used to control the second grid-connected switch and the first grid-connected switch to be attracted when the inverter circuit has been started and the output terminal voltage of the inverter circuit and the grid-side voltage of the power grid meet the grid-connected conditions, so as to enable the photovoltaic power generation system to operate in grid connection.

8. The photovoltaic power generation system according to claim 7, characterized in that: The control unit is used for controlling the second grid-connected switch and the first grid-connected switch to be closed when the grid-connected switch device passes the self-test.

9. The photovoltaic power generation system according to any one of claims 2 to 8, characterized in that: The control unit is also used to output a startup failure alarm message when the residual current detection of the inverter circuit, the insulation impedance detection of the inverter circuit or the self-test of the grid-connected switch device fails.

10. The photovoltaic power generation system according to any one of claims 1 to 8, characterized in that: Also includes: An AC auxiliary power supply, the control unit is connected to the power grid through the AC auxiliary power supply, and the AC auxiliary power supply is used to convert the AC power of the power grid into DC power to supply power to the control unit.

11. The photovoltaic power generation system according to any one of claims 1 to 8, characterized in that: The DC bus capacitor includes a positive bus capacitor and a negative bus capacitor, and one end of the positive bus capacitor and one end of the negative bus capacitor are connected to a bus midpoint.

12. The photovoltaic power generation system according to claim 11, characterized in that: Also includes: A voltage balancing switch device, the voltage balancing switch device comprising a first voltage balancing switch and a second voltage balancing switch, the first end of the charging module is connected to the bus midpoint, the second end of the charging module is connected to the other end of the positive bus capacitor, the third end of the charging module is connected to the other end of the negative bus capacitor, the first voltage balancing switch is arranged between the second end of the charging module and the other end of the positive bus capacitor, and the second voltage balancing switch is arranged between the third end of the charging module and the other end of the negative bus capacitor; The control unit is connected to the voltage balancing switch device, and the control unit is used to control one of the first voltage balancing switch and the second voltage balancing switch to be opened and the other to be closed based on the voltage of the positive bus capacitor and the voltage of the negative bus capacitor when the voltage difference between the positive bus capacitor and the negative bus capacitor is greater than a preset voltage threshold; Among them, when the first voltage balancing switch is closed and the second voltage balancing switch is opened, the charging module charges the positive bus capacitor; when the first voltage balancing switch is opened and the second voltage balancing switch is closed, the charging module charges the negative bus capacitor.

13. The photovoltaic power generation system according to any one of claims 1 to 8, characterized in that: The charging module includes a current limiting resistor and a rectifier circuit connected in series, the current limiting resistor is used to limit the charging current of the DC bus capacitor, and the rectifier circuit is used to charge the DC bus capacitor.

14. The photovoltaic power generation system according to any one of claims 1 to 8, characterized in that: The control unit is also used to output an auxiliary source closing instruction to control the AC starting switch to close so as to charge the DC bus capacitor when the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the grid line voltage plus a threshold and an AC starting instruction is received.

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