Photovoltaic system and breaking device

Abstract

The utility model is suitable for the technical field of power electronics, and provides a photovoltaic system and a breaking device, and the photovoltaic system comprises a photovoltaic string unit, an inverter, a grid-connected switch, and a breaking device. The photovoltaic string unit is connected with the input end of the inverter; the output end of the inverter is connected with the input end of the grid-connected switch; the output end of the grid-connected switch is connected with the input end of the breaking device; the output end of the breaking device is used for being connected with a three-phase power grid. And the breaking device is used for carrying out soft turn-off on the photovoltaic system under the condition of detecting that the three-phase current generated in the photovoltaic system exceeds the rated current. According to the photovoltaic system and the breaking device provided by the utility model, breaking of different levels of short-circuit current is realized.

Description

Technical Field

[0001] The utility model belongs to the technical field of power electronics, and in particular relates to a photovoltaic system and a disconnecting device. Background Art

[0002] With the continuous development of the photovoltaic industry, centralized inverters have emerged as a popular choice for power plant applications due to their high capacity and low cost. Increasing the inverter's power rating or the system voltage increases the overall capacity of the photovoltaic system. However, when a short circuit occurs on the inverter's AC side, it is difficult to isolate the thousands of amperes of current.

[0003] The AC side of a centralized high-voltage photovoltaic system typically uses a frame circuit breaker as the grid-connected switch. This switch physically isolates the grid while also providing the ability to interrupt tens of kiloamperes of current in the event of a grid short-circuit.

[0004] However, this solution has the following problems: First, the mechanical life of the frame circuit breaker is short, up to 10,000 times, and its failure rate shows a normal distribution after more than a few thousand times of occupancy, which is a high failure rate; second, the cost of the frame circuit breaker is high, and in order to meet the ability to break large currents, the frame circuit breaker is now equipped with a special arc extinguishing chamber for arc extinguishing; third, the current frame circuit breaker in the industry does not have a cost-effective solution with the ability to break hundreds of kiloamperes of short-circuit current; fourth, the frame circuit breaker is a mechanical switch with a long closing and disconnecting time, generally more than 20ms. Therefore, it is difficult to implement a centralized inverter solution with a higher system voltage level or a higher capacity. Utility Model Content

[0005] The embodiments of the present utility model provide a photovoltaic system and a disconnecting device, which are intended to solve the problem that a frame circuit breaker cannot adapt to short-circuit faults of photovoltaic systems with higher system voltage levels or higher capacities.

[0006] The utility model provides a photovoltaic system, comprising: a photovoltaic string unit, an inverter, a grid-connected switch and a disconnecting device;

[0007] The photovoltaic string unit is connected to the input end of the inverter; the output end of the inverter is connected to the input end of the grid-connected switch; the output end of the grid-connected switch is connected to the input end of the disconnecting device; the output end of the disconnecting device is used to connect to the three-phase power grid;

[0008] The disconnecting device is used to soft-shut down the photovoltaic system when it is detected that the three-phase current generated in the photovoltaic system exceeds the rated current.

[0009] In some embodiments, the disconnect device includes three power device modules, each power device module includes at least one high-voltage power device;

[0010] The output end of the grid-connected switch is a three-phase output end, each phase output end is connected to the input end of a power device module, and the output end of the power device module is connected to the three-phase power grid;

[0011] Each of the power device modules is used to perform soft switching control on currents of different phases corresponding to the three-phase current.

[0012] In some embodiments, the rated current includes a first rated current corresponding to the power device module, and the power device module is used to control the high-voltage power device to switch from a saturation state to a shutdown state when the current of the corresponding phase exceeds the first rated current.

[0013] In some embodiments, the disconnecting device includes three power device modules and three AC fuses, and each power device module includes at least one high-voltage power device;

[0014] The output end of the grid-connected switch is a three-phase output end, each phase output end is connected to the input end of an AC fuse, the output end of each AC fuse is connected to a power device module, and the output end of the power device module is connected to the three-phase power grid;

[0015] Each power device module is used to perform soft switching control on currents of different phases corresponding to the three-phase current;

[0016] Each of the AC fuses is used to perform hard switching control on the currents of the different phases.

[0017] In some embodiments, the rated current includes a first rated current corresponding to the power device module and a second rated current corresponding to the AC fuse;

[0018] The power device module is used to control the high-voltage power device to switch from a saturation state to a shutdown state when the current of the corresponding phase exceeds the first rated current;

[0019] The AC fuse is configured to be blown when the current of the corresponding phase exceeds the second rated current.

[0020] In some embodiments, the high-voltage power device is an IGBT;

[0021] In the case where the power device module includes four IGBTs, the four IGBTs are connected in series in pairs and then in parallel.

[0022] The present invention also provides a disconnecting device, which is applied to the photovoltaic system as described above, and the disconnecting device includes: an AC fuse and an IGBT module;

[0023] The first end of the AC fuse is used to connect to the grid-connected switch, the second end of the AC fuse is connected to the first end of the IGBT module, the second end of the IGBT module is used to connect to the three-phase power grid, and the IGBT module includes at least one IGBT;

[0024] The IGBT module is used to perform soft switching control on currents of different phases corresponding to the three-phase current;

[0025] The AC fuse is used to perform hard switching control on the currents of the different phases.

[0026] The photovoltaic system and disconnecting device provided by the utility model can quickly perform soft shutdown within microseconds when the generated three-phase current exceeds the rated current by setting a disconnecting device in the photovoltaic system. It can realize the disconnection of small, medium and large levels of short-circuit current at a low cost, and can thus solve the short-circuit disconnection problem on the AC side of higher voltage and higher power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural diagram of a photovoltaic system provided by the prior art;

[0028] Figure 2 This is a schematic structural diagram of a photovoltaic system provided by an embodiment of the present utility model;

[0029] Figure 3 This is one of the structural diagrams of the disconnecting device provided by the embodiment of the present utility model;

[0030] Figure 4 This is the second structural diagram of the disconnecting device provided by the embodiment of the present utility model;

[0031] Figure 5 This is a schematic structural diagram of a disconnecting device applied to a photovoltaic system provided by an embodiment of the present utility model;

[0032] Figure 6 This is one of the structural diagrams of the centralized high-voltage photovoltaic system provided by the embodiment of the present utility model;

[0033] Figure 7 This is the second structural diagram of the centralized high-voltage photovoltaic system provided by the embodiment of the present utility model. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] References to "embodiments" or "implementations" in this disclosure mean that a particular feature, component, or characteristic described in connection with an embodiment or implementation may be included in at least one embodiment of the disclosure. The appearance of such phrases in various places in the specification does not necessarily refer to the same embodiment, nor do they constitute independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0036] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "left", "right", "horizontal", "top", "bottom", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0037] In the description of this utility model, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections, or mutual communication; direct connections or indirect connections through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on specific circumstances.

[0038] In related technologies, with the severe cost problem in the photovoltaic industry, most suppliers reduce costs by increasing the power level of the inverter or increasing the system voltage level. As a result, the power of the inverter in the photovoltaic system is getting larger and larger, and the system voltage level is increased from the original 1000V system to the 1500V system and is moving towards the system above 2000V. Figure 1 In the solution shown, PV panels output DC power through PV string units to the inverter's DC load switch. The IGBT modules in the inverter then modulate the output through software and filter it into a sinusoidal wave. This power is then connected to the three-phase grid via a frame circuit breaker. Using an AC-side frame circuit breaker makes it difficult to implement a centralized inverter solution with higher system voltage levels and capacities.

[0039] The following combination Figure 2-Figure 7 The photovoltaic system and disconnecting device provided by the utility model are described.

[0040] Figure 2 This is a schematic diagram of the structure of the photovoltaic system provided by the embodiment of the present utility model. Figure 2 The photovoltaic system provided by the present utility model includes:

[0041] Photovoltaic string unit 10, inverter 20, grid-connected switch 30 and disconnect device 40;

[0042] The photovoltaic string unit 10 is connected to the input end of the inverter 20; the output end of the inverter 20 is connected to the input end of the grid-connected switch 30; the output end of the grid-connected switch 30 is connected to the input end of the disconnecting device 40; the output end of the disconnecting device 40 is used to connect to the three-phase power grid 50;

[0043] The disconnecting device 40 is used to soft-shut down the photovoltaic system when it is detected that the three-phase current generated in the photovoltaic system exceeds the rated current.

[0044] In practice, PV string unit 10 is a circuit unit consisting of multiple PV panels connected in series to increase output voltage and output current by connecting them in parallel. The number of PV panels in PV string unit 10 depends on system design requirements and is not specifically limited here.

[0045] The inverter 20 is mainly used to convert the direct current generated by the photovoltaic panels into alternating current so as to be connected to the power grid or used by local loads.

[0046] The grid-connected switch 30 is primarily used for connecting to the AC grid of renewable energy power generation systems (such as photovoltaic and wind power systems). The grid-connected switch 30 can be a contactor, load switch, or low-short-circuit current frame circuit breaker. These switches only have low short-circuit current breaking capabilities and are extremely low-cost.

[0047] Existing technologies typically use a frame circuit breaker to connect and disconnect circuits, shutting off the circuit in the event of a grid fault or system anomaly. However, the photovoltaic system provided by the present invention has a disconnect device 40 connected after the grid-connected switch 30. Disconnect device 40 is used to interrupt short-circuit currents, while the grid-connected switch 30 controls the photovoltaic system's grid connection, acting as a physical isolation switch and not responsible for interrupting short-circuit currents.

[0048] It is understood that the photovoltaic system is equipped with short-circuit current detection software. If the software detects that the three-phase current generated in the photovoltaic system exceeds the rated current, the disconnecting device 40 can use a voltage-type device to achieve soft shutdown within microseconds. The rated current refers to the maximum current value that the device used in the disconnecting device 40 can continuously withstand under specific conditions.

[0049] During the rapid shutdown process, the disconnecting device 40 needs to process a current value that may be close to or reach its rated current in a very short time. However, due to its fast switching characteristics, the disconnecting device 40 can effectively control and limit current overshoot and oscillation, thereby protecting the device from damage.

[0050] The photovoltaic system provided by the present invention can quickly perform soft shutdown within microseconds when the generated three-phase current exceeds the rated current by arranging a disconnecting device in the photovoltaic system, and can achieve the disconnection of small, medium and large levels of short-circuit current at a low cost, thereby solving the short-circuit disconnection problem on the AC side of a higher voltage level and higher power system.

[0051] In some embodiments, the disconnect device 40 includes three power device modules, each of which includes at least one high-voltage power device;

[0052] The output end of the grid-connected switch 30 is a three-phase output end, and each phase output end is connected to the input end of a power device module. The output end of the power device module is used to connect to the three-phase power grid 50;

[0053] Each power device module is used to perform soft switching control on currents of different phases corresponding to the three-phase current.

[0054] It will be understood that since inverter 20 outputs three-phase AC power, its output terminals are three-phase output ports. Each phase output terminal of inverter 20 is connected to the three-phase input terminals of grid-connected switch 30. Each phase output terminal of grid-connected switch 30 is connected to a power device module, and the output terminals of each power device module are connected to the three-phase input terminals of three-phase grid 50. Consequently, the current in each phase is controlled by a dedicated power device module, and this control process utilizes soft switching technology. Specifically, each power device module switches the current in the corresponding phase on and off at the appropriate time based on system requirements and instructions.

[0055] Among them, the power device module may include one or more high-voltage power devices. If it includes multiple high-voltage power devices, the connection relationship between the multiple high-voltage power devices can be designed according to actual conditions and is not specifically limited here.

[0056] It should be noted that high-voltage power devices refer to semiconductor devices capable of handling high voltage and high current, including, for example, insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs), or high-power transistors.

[0057] In some embodiments, the rated current includes a first rated current corresponding to the power device module, and the power device module is used to control the high-voltage power device to switch from a saturation state to a shutdown state when the current of the corresponding phase exceeds the first rated current.

[0058] In actual implementation, each power device module has a nominal first rated current. When the current of the corresponding phase exceeds the first rated current, the high-voltage power device in the power device module will desaturate, and the high-voltage power device will switch from the saturation state to the shutdown state.

[0059] It should be noted that in the saturation state, the high-voltage power device is in the on state, and when entering the desaturation state, the high-voltage power device will be turned into the off state.

[0060] In some embodiments, the disconnect device 40 includes three power device modules and three AC fuses, and each power device module includes at least one high-voltage power device;

[0061] The output end of the grid-connected switch 30 is a three-phase output end, each phase output end is connected to the input end of an AC fuse, and the output end of each AC fuse is connected to a power device module, and the output end of the power device module is used to connect to the three-phase grid 50;

[0062] Each power device module is used to perform soft switching control on the currents of different phases corresponding to the three-phase current;

[0063] Each AC fuse is used to perform hard switching control on the current of a different phase.

[0064] Optionally, the disconnecting device may include three AC fuses and three power device modules. The output end of the inverter 20 is a three-phase output port, and each phase output end of the inverter 20 is respectively connected to the three-phase input end of the grid-connected switch 30. Each phase output end of the grid-connected switch 30 is respectively connected to an AC fuse, and the output end of each AC fuse is connected to a power device module. The output end of each power device module is correspondingly connected to the three-phase input end of the three-phase grid 50. The current on each phase is then controlled by a power device module and an AC fuse, and this control process utilizes soft switching technology. Specifically, each power device module will switch the current on the corresponding phase on an appropriate time according to the system's requirements and instructions, and the AC fuse will also switch on and off according to the current on the corresponding phase.

[0065] In some embodiments, the rated current includes a first rated current corresponding to the power device module and a second rated current corresponding to the AC fuse;

[0066] The power device module is used to control the high-voltage power device to switch from a saturation state to a shutdown state when the current of the corresponding phase exceeds a first rated current;

[0067] The AC fuse is used to melt when the current of the corresponding phase exceeds the second rated current.

[0068] In actual implementation, each power device module has a nominal first rated current. When the current of the corresponding phase exceeds the first rated current, the high-voltage power device in the power device module will desaturate, and the high-voltage power device will switch from the saturation state to the shutdown state.

[0069] Each AC fuse has a nominal second rated current. When the current of a corresponding phase exceeds the second rated current, the AC fuse will melt.

[0070] During the desaturation process of high-voltage power devices, the AC fuse will trigger short-circuit disconnection. The cooperation between the two can achieve the disconnection of small, medium and large levels of short-circuit current.

[0071] In some embodiments, the high-voltage power device is an IGBT;

[0072] When the power device module includes four IGBTs, the four IGBTs are connected in series in pairs and then in parallel.

[0073] like Figure 3 As shown, the disconnecting device 40 includes three power device modules 401, each of the three power device modules 401 includes multiple IGBTs, and the power device module 401 on each phase includes four IGBTs. The four IGBTs are grouped in twos and connected in series, and then the two groups of series-connected IGBTs are connected in parallel. Figure 3 The three-phase output terminals of the grid-connected switch 30 are each connected to a power device module 401 , and the output terminal of the disconnecting device 40 is connected to the input terminal of the transformer 60 . The output terminal of the transformer 60 is used to connect to the three-phase grid 50 .

[0074] like Figure 4 As shown, the disconnect device 40 includes three power device modules 401 and three AC fuses 402. An AC fuse 402 is connected in series with a power device module 401. Each power device module 401 includes multiple IGBTs. The power device module 401 on each phase includes four IGBTs. The four IGBTs are grouped in pairs and connected in series. The two groups of series-connected IGBTs are then connected in parallel. Figure 4The three-phase output terminals of the grid-connected switch 30 are each connected to an AC fuse 402, and each AC fuse 402 is connected to a power device module 401. The output terminal of the disconnecting device 40 is connected to the input terminal of the transformer 60, and the output terminal of the transformer 60 is used to connect to the three-phase grid 50.

[0075] Figure 5 This is a schematic diagram of the structure of a disconnecting device for a photovoltaic system provided by an embodiment of the present invention. Figure 5 The disconnecting device 100 provided by the present invention is applied to the photovoltaic system provided by any of the above embodiments. The disconnecting device 100 includes: an AC fuse 1001 and an IGBT module 1002;

[0076] The first end of the AC fuse 1001 is connected to the grid-connected switch, the second end of the AC fuse is connected to the first end of the IGBT module, the second end of the IGBT module 1002 is connected to the three-phase grid, and the IGBT module includes at least one IGBT;

[0077] The IGBT module 1002 is used to perform soft switching control on the currents of different phases corresponding to the three-phase current;

[0078] The AC fuse 1001 is used to perform hard switching control on currents of different phases.

[0079] In actual implementation, when a serious short-circuit current occurs in the photovoltaic system, it is first detected that the short-circuit current exceeds the rated current, and the IGBT module 1002 is turned off first. As a voltage-type device, the IGBT module 1002 can quickly shut down the nominal rated current of the device within microseconds. When the short-circuit current is too large, the desaturation function of the IGBT module 1002 can be used to quickly perform soft shutdown, and then cooperate with the AC fuse 1001. During the desaturation process of the IGBT module 1002, the AC fuse 1001 will trigger short-circuit disconnection. The relevant cooperation between the two can realize the disconnection of small, medium and large short-circuit currents at a low cost. The mutual cooperation can solve the short-circuit disconnection problem on the AC side of higher voltage and higher power systems.

[0080] It can be understood that the IGBT module 1002 includes at least one IGBT.

[0081] When the IGBT module 1002 includes one IGBT, this one IGBT is directly connected in series with the AC fuse 1001; when the IGBT module 1002 includes one IGBT, this one IGBT is directly connected in series with the AC fuse 1001; when the IGBT module 1002 includes multiple IGBTs, the connection method of the multiple IGBTs can be designed according to actual needs and is not specifically limited here.

[0082] For example, when the IGBT module 1002 includes four IGBTs, the four IGBTs are connected in series in pairs and then in parallel.

[0083] The disconnecting device provided in the embodiment of the present invention utilizes the fast shutdown capability and desaturation capability of the IGBT in conjunction with an AC fuse to achieve the disconnection of small, medium, and large short-circuit currents. It is specially used for high-voltage or large-capacity centralized photovoltaic inverters and can effectively solve the problem of strong disconnecting current on the AC side of the photovoltaic system.

[0084] The following describes the embodiments of the present invention in conjunction with actual application scenarios.

[0085] Traditional centralized high-voltage photovoltaic systems such as Figure 6 As shown in the figure, the centralized high-voltage photovoltaic system after adding the disconnect device is as follows Figure 7 The centralized inverter includes: DC load switch, IGBT module, inverter inductor and AC filter capacitor.

[0086] like Figure 6 As shown, the system uses a frame circuit breaker to connect and disconnect the circuit. The frame circuit breaker is also used to cut off the circuit when the power grid fails or the system is abnormal. The photovoltaic system provided by the embodiment of the utility model is as follows. Figure 7 As shown, a disconnect device is connected after the grid-connected switch. The disconnect device is used to interrupt short-circuit currents, while the grid-connected switch is used to control the grid connection of the photovoltaic system. In other words, it acts as a physical isolation switch and does not interrupt short-circuit currents.

[0087] It is understandable that a transformer can be added after the disconnecting device according to actual conditions and then connected to the three-phase power grid, which is not specifically limited here.

[0088] The embodiment of the present utility model proposes a solution for the strong breaking current on the AC side of a centralized high-voltage photovoltaic system. The focus is on a breaking device that is matched with an IGBT module and an AC fuse and is applied to a centralized high-voltage photovoltaic system. The system can be applied to larger-capacity photovoltaic systems with system voltage levels of 1500V and above, effectively solving the problem of strong breaking current on the AC side of a centralized high-voltage photovoltaic system.

[0089] It is understandable that those skilled in the art can, under the guidance of the above embodiments, combine various implementation methods in the above embodiments to obtain technical solutions of multiple implementation methods.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A photovoltaic system, characterized in that: include: PV string units, inverters, grid-connected switches and disconnect devices; The photovoltaic string unit is connected to the input end of the inverter; the output end of the inverter is connected to the input end of the grid-connected switch; The output end of the grid-connected switch is connected to the input end of the disconnecting device; the output end of the disconnecting device is used to be connected to the three-phase power grid; The disconnecting device is used to soft-shut down the photovoltaic system when it is detected that the three-phase current generated in the photovoltaic system exceeds the rated current.

2. The photovoltaic system according to claim 1, characterized in that: The disconnecting device includes three power device modules, each power device module includes at least one high-voltage power device; The output end of the grid-connected switch is a three-phase output end, each phase output end is connected to the input end of a power device module, and the output end of the power device module is connected to the three-phase power grid; Each of the power device modules is used to perform soft switching control on currents of different phases corresponding to the three-phase current.

3. The photovoltaic system according to claim 2, characterized in that: The rated current includes a first rated current corresponding to the power device module, and the power device module is used to control the high-voltage power device to switch from a saturation state to a shutdown state when the current of the corresponding phase exceeds the first rated current.

4. The photovoltaic system according to claim 1, characterized in that: The disconnecting device includes three power device modules and three AC fuses, and each power device module includes at least one high-voltage power device; The output end of the grid-connected switch is a three-phase output end, each phase output end is connected to the input end of an AC fuse, the output end of each AC fuse is connected to a power device module, and the output end of the power device module is connected to the three-phase power grid; Each power device module is used to perform soft switching control on currents of different phases corresponding to the three-phase current; Each of the AC fuses is used to perform hard switching control on the currents of the different phases.

5. The photovoltaic system according to claim 4, characterized in that: The rated current includes a first rated current corresponding to the power device module and a second rated current corresponding to the AC fuse; The power device module is used to control the high-voltage power device to switch from a saturation state to a shutdown state when the current of the corresponding phase exceeds the first rated current; The AC fuse is configured to be blown when the current of the corresponding phase exceeds the second rated current.

6. The photovoltaic system according to any one of claims 2 to 5, characterized in that: The high-voltage power device is an IGBT; In the case where the power device module includes four IGBTs, the four IGBTs are connected in series in pairs and then in parallel.

7. A breaking device, characterized in that: Applicable to the photovoltaic system according to any one of claims 1 to 6, the disconnecting device comprises: an AC fuse and an IGBT module; The first end of the AC fuse is used to connect to the grid-connected switch, the second end of the AC fuse is connected to the first end of the IGBT module, the second end of the IGBT module is used to connect to the three-phase power grid, and the IGBT module includes at least one IGBT; The IGBT module is used to perform soft switching control on currents of different phases corresponding to the three-phase current; The AC fuse is used to perform hard switching control on the currents of the different phases.

8. The breaking device according to claim 7, characterized in that: In the case that the IGBT module includes four IGBTs, the four IGBTs are connected in series in pairs and then in parallel.

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