CN215835136U

CN215835136U - Photovoltaic grid-connected system

Info

Publication number: CN215835136U
Application number: CN202121488912.XU
Authority: CN
Inventors: 魏学良; 符含润; 曹旭东
Original assignee: China University of Petroleum Beijing
Current assignee: China University of Petroleum Beijing
Priority date: 2021-07-01
Filing date: 2021-07-01
Publication date: 2022-02-15
Anticipated expiration: 2031-07-01

Abstract

This specification discloses a photovoltaic grid-connected system includes: at least three bidirectional DC/DC modules; the direct current side of each bidirectional DC/AC module is connected with the first side of at least one bidirectional DC/DC module, and the second side of each bidirectional DC/DC module is used for connecting a photovoltaic power generation device or an energy storage device; the alternating current side of each bidirectional DC/AC module is connected to one alternating current bus, and each alternating current bus is connected with at least one bidirectional DC/AC module; a switching device, comprising: the first wiring terminal is connected to an alternating current bus, and the second wiring terminal is used for connecting a mains supply power grid; two ends of the controlled side of each controllable switch are respectively connected with a first wiring terminal and a second wiring terminal; the controller is connected with at least three controllable switches. The system can incorporate the electric energy generated by the photovoltaic power generation device into a three-phase circuit of a mains supply power grid.

Description

Photovoltaic grid-connected system

Technical Field

The application relates to the technical field of photovoltaics, in particular to a photovoltaic grid-connected system.

Background

Photovoltaic power generation is widely used as a clean power generation mode, and the photovoltaic power generation technology is to directly convert light energy into electric energy by utilizing the photovoltaic effect of a semiconductor interface. The photovoltaic cell panels are main components of a photovoltaic power generation system, the photovoltaic cell panels are connected in series and then are packaged and protected to form a large-area photovoltaic cell assembly, and the photovoltaic power generation device is formed by matching with components such as a power controller and the like.

The electric energy generated by the existing distributed photovoltaic power generation device is generally merged into one phase circuit of the commercial power grid, however, when the photovoltaic power generation power is large, the grid connection mode easily causes the three-phase power of the commercial power grid to be unbalanced.

In view of the above problems, no effective solution has been proposed.

SUMMERY OF THE UTILITY MODEL

The purpose of the embodiment of the application is to provide a photovoltaic grid-connected system to realize the three-phase circuit that incorporates the electric energy generated by the photovoltaic power generation device into the commercial power grid.

In order to solve the above technical problem, an embodiment of the present specification provides a photovoltaic grid-connected system, including: at least three bidirectional DC/DC modules, each bidirectional DC/DC module including a first side and a second side for boosting or stepping down; the system comprises at least three bidirectional DC/AC modules, wherein the direct current side of each bidirectional DC/AC module is connected with the first side of at least one bidirectional DC/DC module, the second side of each bidirectional DC/AC module is used for connecting a photovoltaic power generation device or an energy storage device, and the bidirectional DC/AC modules are used for realizing the conversion of direct current and alternating current; the alternating current side of each bidirectional DC/AC module is connected to one alternating current bus, and each alternating current bus is connected with at least one bidirectional DC/AC module; a switching device, comprising: the alternating current bus bar comprises a first wiring terminal, a second wiring terminal, at least three controllable switches and a controller, wherein the first wiring terminal is connected to an alternating current bus bar, and the second wiring terminal is used for connecting a commercial power grid; the two ends of the controlled side of each controllable switch are respectively connected with the first wiring terminal and the second wiring terminal; the controller is connected with the control ends of the at least three controllable switches and used for outputting control signals to control the current flowing through the controlled sides of the at least three controllable switches.

According to the photovoltaic grid-connected system provided by the embodiment of the specification, the bidirectional DC/DC module, the bidirectional DC/AC module, the three alternating-current buses and the switching device comprising the at least two wiring terminals and the at least three controllable switches are arranged, so that the mode that electric energy generated by the photovoltaic power generation device is merged into a mains supply power grid in a three-phase mode is realized, and the problem of three-phase imbalance of the mains supply power grid caused by a single-phase grid-connected mode is solved.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only some embodiments described in the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 shows a schematic diagram of a photovoltaic grid-connected system provided according to an embodiment of the present disclosure;

fig. 2 shows a schematic view of the internal structure of the switching device;

FIGS. 3A and 3B are schematic diagrams of the current path for electrical energy flowing from the photovoltaic power plant or energy storage cell side to the AC bus side;

FIGS. 3C and 3D are schematic diagrams of the current path for electrical energy flowing from the AC bus side to the photovoltaic power plant or energy storage cell side;

fig. 4 shows a circuit schematic of a bi-directional DC/AC module.

Detailed Description

In order to make those skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive work based on the embodiments in the present application shall fall within the scope of protection of the present application.

Fig. 1 shows a schematic diagram of a photovoltaic grid-connected system provided according to an embodiment of the present disclosure. The photovoltaic grid-connected system can be used for feeding electric energy generated by the photovoltaic cell panel regulated by the power controller into a three-phase commercial power grid. The utility grid may be 220V, 380V, or other specified voltage levels. As shown in fig. 1, the photovoltaic grid-connected system includes at least three bidirectional DC/DC modules, at least three bidirectional DC/AC modules, three AC buses, and a switching device, wherein the switching device includes a first connection terminal, a second connection terminal, at least three controllable switches, and a controller. Fig. 2 shows a schematic view of the internal structure of the switching device.

Each bidirectional DC/DC module includes a first side and a second side for boosting or stepping down. As shown in fig. 1, when the electric energy generated by the photovoltaic power generation device needs to be fed into the utility grid, the bidirectional DC/DC module is used to raise the output voltage of the photovoltaic power generation device to a predetermined voltage level. For example, to 110V, 120V, 220V, 230V, 380V, etc. When it is desired to charge the energy storage device via the bus or the utility grid, the voltage from the bus side is stepped down to a predetermined voltage level. For example, down to a charging voltage level of the energy storage device, such as 36V, 48V, etc. The photovoltaic power generation device described in this specification includes a photovoltaic cell panel and a power controller.

The bidirectional DC/AC module is used for realizing conversion of direct current and alternating current, namely converting direct current generated by the photovoltaic power generation device into alternating current, or charging the energy storage device by alternating current from one side of the bus. The alternating current from one side of the bus can be electricity from a commercial power grid or electricity generated by other photovoltaic power generation devices.

As shown in fig. 1, the DC side of each bi-directional DC/AC module is connected to a first side of at least one bi-directional DC/DC module, and a second side of the bi-directional DC/DC module is used to connect to a photovoltaic power generation device or an energy storage device. When the number of bidirectional DC/DC modules connected to the DC side of one bidirectional DC/AC module is greater than or equal to two, the output terminals of the first side of these bidirectional DC/DC modules may be connected in the manner of a bus, and the bus connects the DC sides of the bidirectional DC/AC modules. This arrangement may increase the power input to the DC side of the bi-directional DC/AC module or reduce the requirement for charging voltage of the energy storage device.

The three alternating current buses respectively correspond to three phases of power of a mains supply power grid. The AC side of each bidirectional DC/AC module is connected to an AC bus, and each AC bus is connected to at least one bidirectional DC/AC module. In fig. 1 a schematic diagram of a three-phase four-wire is shown, i.e. the bus bar comprises, in addition to the three-phase live wire, a ground wire N, corresponding to the connection terminal in fig. 2. One end of the alternating current output side of each bidirectional DC/AC module is connected to the grounding wire N, and the other end of the alternating current output side of each bidirectional DC/AC module is connected to the live wire bus of one phase. Therefore, the photovoltaic grid-connected system is suitable for being incorporated into a three-phase four-wire system power grid system.

As shown in fig. 2, the two connection terminals of the switching device have four sets of terminals, respectively, each set includes two terminals, and the two terminals in each set are connected by a wire. One set of terminals corresponds to one bus bar, and the first terminal of each set of the first terminal 1 and the second terminal 2 is connected to the controllable switch. In the first connecting terminal, a second connecting terminal in a group of connecting terminals is used for connecting an alternating current bus; in the second connection terminal, a second connection terminal of the group of connection terminals is used for connecting a mains supply network.

And two ends of the controlled side of each controllable switch are respectively connected with the first connecting terminal and the second connecting terminal. In this specification, a control terminal of the controllable switch is used for connecting a controller to receive a control signal; when the control signal changes, the on or off state of the controllable switch changes.

The controller and the control ends of the at least three controllable switches are used for outputting control signals to control the current flowing through the controlled sides of the at least three controllable switches. The at least three controllable switches may be IGBTs or thyristors, and when the mains voltage is high, thyristors may be used as the controllable switches.

In some embodiments, at least three controllable switches are disposed on the heat sink Ra to improve heat dissipation capability and prevent device damage in consideration of high current and high power during grid connection. The fan can be arranged adjacent to at least three controllable switches, the fan is arranged towards the controllable switches, and the control end of the fan is connected with the controller, so that the controller can control the starting and stopping of the fan, and the heat dissipation of the three controllable switches is further realized.

It should be noted that, in fig. 2, a Power module Power is further provided to supply Power to the modules or devices such as the Controller, the transformer Tr, the controllable switch SW, the Fan, the LCD display, and the LED display, and in order to make the lines clearly recognizable, the Power supply line is not illustrated in fig. 2.

According to the photovoltaic grid-connected system, the bidirectional DC/DC module, the bidirectional DC/AC module, the three alternating current buses and the switching device comprising the at least two wiring terminals and the at least three controllable switches are arranged, so that the mode that electric energy generated by the photovoltaic power generation device is merged into a commercial power grid in a three-phase mode is realized, and the problem of three-phase imbalance of the commercial power grid caused by a single-phase grid-connected mode is solved.

In some embodiments, the DC side of each bi-directional DC/AC module is connected to a first side of at least two bi-directional DC/DC modules, wherein the second side of at least one bi-directional DC/DC module is connected to the photovoltaic power generation device and the second side of at least one bi-directional DC/DC module is connected to the energy storage device, such that each bi-directional DC/AC module can both enable the photovoltaic power generation device to access the utility grid and charge the energy storage device with AC power from one side of the bus. The alternating current from one side of the bus can be electricity from a commercial power grid or electricity generated by other photovoltaic power generation devices.

In some embodiments, the DC side of each bi-directional DC/AC module is connected to a first side of at least two bi-directional DC/DC modules, and the second sides of at least two bi-directional DC/DC modules may be connected to a photovoltaic power generation device, respectively, or the second sides of at least two bi-directional DC/DC modules may be connected to an energy storage device, respectively, as shown in fig. 1. Under the condition that each of the three alternating current buses is connected with one photovoltaic power generation device through the bidirectional DC/DC module and the bidirectional DC/AC module, the photovoltaic power generation device or the energy storage device can be connected with the second side of any bidirectional DC/DC module, and the embodiment of the specification does not limit the photovoltaic power generation device or the energy storage device.

In some embodiments, a DC/DC module may be fixed to operate in a boost mode, or fixed to operate in a buck mode, and may not be adjustable. For example, a DC/DC module connected to a photovoltaic power generation device operates in a boost mode and a DC/DC module connected to an energy storage device operates in a buck mode. The step-up or step-down as used herein refers to a voltage increase or decrease when the voltage is switched from the second side to the first side of the DC/DC module.

In some embodiments, the DC/DC module can operate in either a boost mode or a buck mode, the mode of operation and the target voltage after boosting or buck being controllable. Specifically, as shown in fig. 3A and 3B, the bidirectional DC/DC module may include a first bridge circuit, a second bridge circuit, and a transformer.

The first bridge circuit comprises a first controllable switch Q1, a second controllable switch Q2, a third controllable switch Q3 and a fourth controllable switch Q4. The second terminal of the controlled side of the first controllable switch Q1 is connected to the first terminal of the controlled side of the third controllable switch Q3, and the second terminal of the controlled side of the second controllable switch Q2 is connected to the first terminal of the controlled side of the fourth controllable switch Q4. A first terminal of the controlled side of the first controllable switch Q1 is connected to a first terminal of the controlled side of the second controllable switch Q2, and a second terminal of the controlled side of the third controllable switch Q3 is connected to a second terminal of the controlled side of the fourth controllable switch Q4. The first end of the controlled side of the first controllable switch Q1 and the second end of the controlled side of the third controllable switch Q3 are respectively used as two connection ends of the second side of the bidirectional DC/DC module.

The second bridge circuit comprises a fifth controllable switch Q5, a sixth controllable switch Q6, a seventh controllable switch Q7, an eighth controllable switch Q8. The second terminal of the controlled side of the fifth controllable switch Q5 is connected to the first terminal of the controlled side of the seventh controllable switch Q7, and the second terminal of the controlled side of the sixth controllable switch Q6 is connected to the first terminal of the controlled side of the eighth controllable switch Q8. A first terminal of the controlled side of the fifth controllable switch Q5 is connected to a first terminal of the controlled side of the sixth controllable switch Q6, and a second terminal of the controlled side of the seventh controllable switch Q7 is connected to a second terminal of the controlled side of the eighth controllable switch Q8. The first end of the controlled side of the sixth controllable switch Q6 and the second end of the controlled side of the eighth controllable switch Q8 are respectively used as two connection ends of the first side of the bidirectional DC/DC module.

A first terminal of a first side of the transformer is connected between the second terminal of the controlled side of the first controllable switch Q1 and the first terminal of the controlled side of the third controllable switch Q3, and a second terminal of a side of the transformer is connected between the second terminal of the controlled side of the second controllable switch Q2 and the first terminal of the controlled side of the fourth controllable switch Q4. A first terminal of the second side of the transformer is connected between the second terminal of the controlled side of the fifth controllable switch Q5 and the first terminal of the controlled side of the seventh controllable switch Q7, and a second terminal of the second side of the transformer is connected between the second terminal of the controlled side of the sixth controllable switch Q6 and the first terminal of the controlled side of the eighth controllable switch Q8.

In this specification, the control end of each controllable switch in the bidirectional DC/DC module is connected to the controller to receive the control signal; when the control signal changes, the electrical signal output by the controlled side or the two controlled ends of the controllable switch changes, for example, becomes larger, smaller (in this case, the controlled side is in an on state), or even 0 (that is, the controlled side is in an off state). The controller connected to each controllable switch in the bidirectional DC/DC module and the controller in the switching device may be one controller or different controllers, which is not limited in this specification.

The circuit principle of the bidirectional DC/DC module to realize bidirectional DC/DC conversion under the control of the controller is described below.

Fig. 3A and 3B are schematic diagrams showing a current path of electric energy flowing from the side of the photovoltaic power generation device or the energy storage battery to the side of the alternating current bus, fig. 3C and 3D are schematic diagrams showing a current path of electric energy flowing from the side of the alternating current bus to the side of the photovoltaic power generation device or the energy storage battery, wherein a bold line and an arrow on the line indicate a current flow direction, BAT + BAT "indicates a positive electrode and a negative electrode connected to the photovoltaic power generation device, respectively, and DC + and DC" indicate two output ends of the bidirectional DC/DC near the side of the alternating current bus, respectively.

When the electric energy generated by the photovoltaic power generation device needs to be converged into an alternating current bus, as shown in fig. 3A, on the left side of a transformer T2, the first controllable switch Q1 and the fourth controllable switch Q4 are controlled to be turned on, and the second controllable switch Q2 and the third controllable switch Q3 are controlled to be turned off, so that the current on the left side of the transformer T2 flows to the direction shown in the figure; as shown in fig. 3B, the second controllable switch Q2 and the third controllable switch Q3 are then controlled to be on, and the first controllable switch Q1 and the fourth controllable switch Q4 are controlled to be off, and the current on the left side of the transformer T2 flows as shown in the figure. The two control modes are executed circularly. Comparing the current flow direction of the left coil of the transformer T2 in fig. 3A and fig. 3B, the dc current is converted into the ac current by controlling the on and off of the four controllable switches on the left side, so that the voltage can be further boosted by the transformer.

As shown in fig. 3A, when the first controllable switch Q1 and the fourth controllable switch Q4 are turned on and the second controllable switch Q2 and the third controllable switch Q3 are turned off, the fifth controllable switch Q5 and the eighth controllable switch Q8 are controlled to be turned on and the sixth controllable switch Q6 and the seventh controllable switch Q7 are controlled to be turned off at the right side of the transformer T2, and the current flow at the right side of the transformer T2 is as shown in the figure; as shown in fig. 3B, when the second controllable switch Q2 and the third controllable switch Q3 are turned on and the first controllable switch Q1 and the fourth controllable switch Q4 are turned off, the sixth controllable switch Q6 and the seventh controllable switch Q7 are controlled to be turned on at the right side of the transformer T2, and the fifth controllable switch Q5 and the eighth controllable switch Q8 are controlled to be turned off, and the current flow at the right side of the transformer T2 is as shown in the figure. The two control modes are executed circularly. Comparing the current flow direction of the coil at the right side of the transformer T2 in fig. 3A and 3B, the conversion of the alternating current into the direct current is realized by controlling the on and off of the four controllable switches at the right side.

When the energy storage battery is charged by the electric energy from one side of the ac bus, as shown in fig. 3C, on the right side of the transformer T2, the sixth controllable switch Q6 and the seventh controllable switch Q7 are first controlled to be on, and the fifth controllable switch Q5 and the eighth controllable switch Q8 are controlled to be off, and the current on the right side of the transformer T2 flows as shown in the figure; as shown in fig. 3D, the fifth controllable switch Q5 and the eighth controllable switch Q8 are then controlled to be on, and the sixth controllable switch Q6 and the seventh controllable switch Q7 are controlled to be off, and the current on the right side of the transformer T2 flows as shown in the figure. The two control modes are executed circularly. Comparing the current flow direction of the coil at the right side of the transformer T2 in fig. 3C and fig. 3D, the dc current is converted into the ac current by controlling the on and off of the four controllable switches at the right side, so that the voltage can be further reduced through the transformer.

As shown in fig. 3C, when the sixth controllable switch Q6 and the seventh controllable switch Q7 are turned on and the fifth controllable switch Q5 and the eighth controllable switch Q8 are turned off, the first controllable switch Q1 and the fourth controllable switch Q4 are controlled to be turned on and the second controllable switch Q2 and the third controllable switch Q3 are controlled to be turned off on the left side of the transformer T2, and the current flow on the left side of the transformer T2 is as shown in the figure; when the fifth controllable switch Q5 and the eighth controllable switch Q8 are turned on and the sixth controllable switch Q6 and the seventh controllable switch Q7 are turned off as shown in fig. 3D, the second controllable switch Q2 and the third controllable switch Q3 are controlled to be turned on and the first controllable switch Q1 and the fourth controllable switch Q4 are controlled to be turned off at the left side of the transformer T2, and the current flow at the left side of the transformer T2 is as shown in the figure. The two control modes are executed circularly. Comparing the current flowing direction of the coil at the right side of the transformer T2 in fig. 3C and fig. 3D, the conversion of the alternating current into the direct current is realized by controlling the on and off of the four controllable switches at the right side.

In some embodiments, the bidirectional DC/DC module may also be implemented by using other types of circuits, such as a circuit using Boost/Buck principle, which is not described in detail in this specification.

In some embodiments, the bidirectional DC/AC module includes a third bridge circuit. Specifically, as shown in fig. 4, a ninth controllable switch Q9, a tenth controllable switch Q10, an eleventh controllable switch Q11, a twelfth controllable switch Q12 are included; a second terminal of the controlled side of the ninth controllable switch Q9 is connected to a first terminal of the controlled side of the eleventh controllable switch Q11, and a second terminal of the controlled side of the tenth controllable switch Q10 is connected to a first terminal of the controlled side of the twelfth controllable switch Q12; a first terminal of a controlled side of the ninth controllable switch Q9 is connected to a first terminal of a controlled side of the tenth controllable switch Q10, and a second terminal of a controlled side of the eleventh controllable switch Q11 is connected to a second terminal of a controlled side of the twelfth controllable switch Q12; the first end of the controlled side of the ninth controllable switch Q9 and the second end of the controlled side of the eleventh controllable switch Q11 are respectively used as two connection ends of the direct current side of the bidirectional DC/AC module, and the two connection ends of the alternating current side of the bidirectional DC/AC module are respectively arranged between the second end of the controlled side of the ninth controllable switch Q9 and the first end of the controlled side of the eleventh controllable switch Q11, and between the second end of the controlled side of the tenth controllable switch Q10 and the first end of the controlled side of the twelfth controllable switch Q12.

The working principle and the internal current flow direction of the bidirectional DC/AC module can be explained with reference to fig. 3A to 3D, and are not described again.

Of course, the bidirectional DC/AC module can also be implemented by using other types of circuits, and the description is not repeated.

The controllable switches in the bidirectional DC/AC module may be connected to a controller to control the controllable switches to be turned on or off. The controller in the controller and the controller in the switching device may be one controller or may be different controllers, which is not limited in this specification.

In some embodiments, a diode, a resistor, and a relay are also disposed between the second side of the bi-directional DC/DC module and the photovoltaic power generation device or the energy storage device. As shown in fig. 3A to 3D, the diode and the resistor are connected in series, the formed series circuit is located in the circuit on the second side of the bidirectional DC/DC module, the controlled terminal of the relay is connected in parallel with the series circuit formed by the diode and the resistor, and the control terminal of the relay is connected to the controller. In this specification, the control end of the relay is used for connecting the controller to receive the control signal; the controlled terminal is closed or opened in response to a change in the control signal.

As shown in fig. 3A to 3D, the relay RLY has pins 1 to 4, where pins 3 and 4 are control terminal pins, and are connected to the controller;

pins

1 and 2 are controlled terminals and are connected to a controlled circuit, namely, are arranged in parallel with a series circuit of a diode and a resistor. When the circuit is started, the relay is controlled to be switched off firstly, and the current flows through the diode and the resistor R51, so that the flow direction of the circuit can be limited, and the photovoltaic power generation device is prevented from being damaged by the backward flow of the current; the voltage can be divided by the resistor R51, so that the energy storage battery is prevented from being damaged due to overlarge current when the energy storage battery is charged.

In some embodiments, the grid-connected photovoltaic system further includes a common mode inductor including a first coil and a second coil wound in opposite directions on the same core. For example, in the common mode inductor L2 shown in fig. 3A to 3D, the first end of the first coil is used for connecting to the first end of the second side of the bidirectional DC/DC module, and the second end of the first coil is used for connecting to the first end of the photovoltaic power generation device or the energy storage device; the first end of the second coil is used for being connected with the second end of the second side of the bidirectional DC/DC module, and the second end of the second coil is used for being connected with the second end of the photovoltaic power generation device or the energy storage device. Or, for example, the common mode inductor L3 in fig. 3A to 3D has a first end of the first coil for connecting to a first end of the first side of the bidirectional DC/DC module, and a second end of the first coil for connecting to one live line in the ac bus; the first end of the second coil is used for being connected with the second end of the first side of the bidirectional DC/DC module, and the second end of the second coil is used for being connected with a grounding wire in the alternating current bus.

The common mode inductance may also be L4 or L5 in fig. 4. By arranging the common-mode inductor, the noise from a power grid or photovoltaic power generation equipment can be effectively suppressed, and the anti-interference capability and reliability of the photovoltaic grid-connected system are improved.

The controllable switch in the specification can be a thyristor, an IGBT or controllable silicon, and the type of the product can be selected according to specific requirements.

In some embodiments, the grid-connected photovoltaic system further comprises a load access terminal, wherein the terminal of the first side is connected with the three-phase alternating current bus, and the terminal of the second side is used for connecting the three-phase load. Through the arrangement, the electric energy generated by the photovoltaic power generation device or the electric energy stored by the energy storage battery can supply power for the local load.

Although the present application has been described in terms of embodiments, those of ordinary skill in the art will recognize that there are numerous variations and permutations of the present application without departing from the spirit of the application, and it is intended that the appended claims encompass such variations and permutations without departing from the spirit of the application.

Claims

1. A grid-connected photovoltaic system, comprising:

at least three bidirectional DC/DC modules, each bidirectional DC/DC module including a first side and a second side for boosting or stepping down;

the system comprises at least three bidirectional DC/AC modules, wherein the direct current side of each bidirectional DC/AC module is connected with the first side of at least one bidirectional DC/DC module, the second side of each bidirectional DC/AC module is used for connecting a photovoltaic power generation device or an energy storage device, and the bidirectional DC/AC modules are used for realizing the conversion of direct current and alternating current;

the alternating current side of each bidirectional DC/AC module is connected to one alternating current bus, and each alternating current bus is connected with at least one bidirectional DC/AC module;

a switching device, comprising: the alternating current bus bar comprises a first wiring terminal, a second wiring terminal, at least three controllable switches and a controller, wherein the first wiring terminal is connected to an alternating current bus bar, and the second wiring terminal is used for connecting a commercial power grid; the two ends of the controlled side of each controllable switch are respectively connected with the first wiring terminal and the second wiring terminal; the controller is connected with the control ends of the at least three controllable switches and used for outputting control signals to control the at least three controllable switches to be switched on or switched off.

2. The grid-connection system according to claim 1, wherein the DC side of each bi-directional DC/AC module is connected to a first side of at least two bi-directional DC/DC modules, wherein a second side of at least one bi-directional DC/DC module is connected to a photovoltaic power generation device and a second side of at least one bi-directional DC/DC module is connected to an energy storage device.

3. The grid-connected photovoltaic system of claim 1, wherein the bi-directional DC/DC module comprises:

the first bridge circuit comprises a first controllable switch, a second controllable switch, a third controllable switch and a fourth controllable switch; the second end of the controlled side of the first controllable switch is connected with the first end of the controlled side of the third controllable switch, and the second end of the controlled side of the second controllable switch is connected with the first end of the controlled side of the fourth controllable switch; a first end of the controlled side of the first controllable switch is connected with a first end of the controlled side of the second controllable switch, and a second end of the controlled side of the third controllable switch is connected with a second end of the controlled side of the fourth controllable switch; a first end of the controlled side of the first controllable switch and a second end of the controlled side of the third controllable switch are respectively used as two connecting ends of a second side of the bidirectional DC/DC module;

the second bridge circuit comprises a fifth controllable switch, a sixth controllable switch, a seventh controllable switch and an eighth controllable switch; a second end of the controlled side of the fifth controllable switch is connected with a first end of the controlled side of the seventh controllable switch, and a second end of the controlled side of the sixth controllable switch is connected with a first end of the controlled side of the eighth controllable switch; a first end of the controlled side of the fifth controllable switch is connected with a first end of the controlled side of the sixth controllable switch, and a second end of the controlled side of the seventh controllable switch is connected with a second end of the controlled side of the eighth controllable switch; a first end of the controlled side of the sixth controllable switch and a second end of the controlled side of the eighth controllable switch are respectively used as two connection ends of the first side of the bidirectional DC/DC module;

a first end of a first side of the transformer is connected between a second end of the controlled side of the first controllable switch and a first end of the controlled side of the third controllable switch, and a second end of the first side of the transformer is connected between a second end of the controlled side of the second controllable switch and a first end of the controlled side of the fourth controllable switch; the first end of the second side of the transformer is connected between the second end of the controlled side of the fifth controllable switch and the first end of the controlled side of the seventh controllable switch, and the second end of the second side of the transformer is connected between the second end of the controlled side of the sixth controllable switch and the first end of the controlled side of the eighth controllable switch.

4. The grid-connected photovoltaic system of claim 1, wherein the bi-directional DC/AC module comprises:

the third bridge circuit comprises a ninth controllable switch, a tenth controllable switch, an eleventh controllable switch and a twelfth controllable switch; a second end of the controlled side of the ninth controllable switch is connected with a first end of the controlled side of the eleventh controllable switch, and a second end of the controlled side of the tenth controllable switch is connected with a first end of the controlled side of the twelfth controllable switch; a first end of the controlled side of the ninth controllable switch is connected with a first end of the controlled side of the tenth controllable switch, and a second end of the controlled side of the eleventh controllable switch is connected with a second end of the controlled side of the twelfth controllable switch; the first end of the controlled side of the ninth controllable switch and the second end of the controlled side of the eleventh controllable switch are respectively used as two connection ends of the direct current side of the bidirectional DC/AC module, and the two connection ends of the alternating current side of the bidirectional DC/AC module are respectively arranged between the second end of the controlled side of the ninth controllable switch and the first end of the controlled side of the eleventh controllable switch and between the second end of the controlled side of the tenth controllable switch and the first end of the controlled side of the twelfth controllable switch.

5. The grid-connected PV system of claim 1, wherein there are further provided between the second side of the bi-directional DC/DC module and the PV power generation device or the energy storage device:

a diode;

a resistor connected in series with the diode, the diode and resistor forming a series circuit in the circuit on the second side of the bidirectional DC/DC module

The controlled end of the relay is connected in parallel with a series circuit formed by the diode and the resistor;

wherein the control end of the relay is connected to the controller.

6. The grid-connected photovoltaic system according to claim 1, further comprising: the common-mode inductor comprises a first coil and a second coil which are wound on the same magnetic core in opposite directions; wherein the content of the first and second substances,

the first end of the first coil is used for being connected with the first end of the second side of the bidirectional DC/DC module, and the second end of the first coil is used for being connected with the first end of the photovoltaic power generation device or the energy storage device; the first end of the second coil is used for being connected with the second end of the second side of the bidirectional DC/DC module, and the second end of the second coil is used for being connected with the second end of the photovoltaic power generation device or the energy storage device; and/or the presence of a gas in the gas,

the first end of the first coil is used for being connected with the first end of the first side of the bidirectional DC/DC module, and the second end of the first coil is used for being connected with one live wire in the alternating current bus; the first end of the second coil is used for being connected with the second end of the first side of the bidirectional DC/DC module, and the second end of the second coil is used for being connected with a grounding wire in the alternating current bus.

7. The grid-connected photovoltaic system of claim 1, wherein the controllable switches comprise at least one of thyristors, IGBTs, and thyristors.

8. The grid-connected photovoltaic system of claim 1, wherein the at least three controllable switches are disposed on a heat sink.

9. The grid-connected photovoltaic system according to claim 1, further comprising:

a fan adjacent to and disposed toward the at least three controllable switches; and the control end of the fan is connected with the controller.

10. The grid-connected photovoltaic system according to claim 1, further comprising: and the terminal of the first side is connected with a three-phase alternating current bus, and the terminal of the second side is used for connecting a three-phase load.