Anti-backflow system for photovoltaic module-level power electronics

Abstract

The utility model relates to photovoltaic power generation technical field, concretely relates to photovoltaic module level power electronic equipment's anti back -in system. System includes controller and anti -backflow diode, the input of controller is connected with each photovoltaic group string's negative pole DC bus, the output of controller is connected with the cathode of anti -backflow diode, the anode of anti -backflow diode is connected with the PV negative pole mouth of inverter, can effectively prevent the back -in problem of the voltage difference of the same road MPPT between different photovoltaic group strings, guarantees the stable operation of MLPE equipment, thereby promotes the stability and reliability of photovoltaic system.

Description

Technical Field

[0001] This utility model relates to the field of photovoltaic power generation technology, specifically to an anti-backflow system for photovoltaic module-level power electronic equipment. Background Technology

[0002] Due to the renewable and clean nature of solar energy, photovoltaic grid-connected power generation technology has developed rapidly. Currently, photovoltaic (PV) systems typically consist of multiple PV modules connected in series to form PV strings. These PV strings are then connected in parallel to form a single input channel to the inverter's Maximum Power Point Tracking (MPPT). Here, "MPPT" refers to the inverter's MPPT input channel (multiple channels can be configured according to actual needs). This is an independent maximum power point tracking (MPPT) control circuit within the inverter. Each MPPT channel can connect to multiple parallel PV strings, adjusting all strings under that channel to operate near their maximum power point. The goal is to increase current without increasing bus voltage, thereby increasing power. This power is then converted into AC by the inverter and transmitted to the grid. Furthermore, to improve the safety of PV systems, existing PV systems typically connect an MLPE (Module-Level Power Electronics, such as a shutdown device or optimizer) after each PV module. The MLPE controls the power output of each PV module. The MLPEs are connected in series and then connected to the inverter's PV port. That is, the negative DC bus of each PV string is connected to the inverter's negative PV port, and the positive PV port of the inverter is connected to the positive DC bus of each PV string.

[0003] However, under the same MPPT, different photovoltaic strings will inevitably form a certain pressure difference due to shading or the degradation of the modules themselves. When the pressure difference is large, the high-voltage string will backflow into the low-voltage string during the inverter commissioning process. This backflow pressure difference will have an adverse impact on the MLPE equipment of the low-voltage string, change the characteristics of the device, and cause the MLPE equipment to be unstable or even damaged. Utility Model Content

[0004] To address the aforementioned technical problems, this utility model proposes an anti-backflow system for photovoltaic module-level power electronic equipment. This system aims to effectively prevent backflow issues between different photovoltaic strings within the same MPPT due to voltage differences, ensuring the stable operation of the MLPE equipment and thereby improving the stability and reliability of the photovoltaic system.

[0005] This application provides a backflow prevention system for photovoltaic module-level power electronic equipment, including a controller and an anti-reverse current diode. The input terminal of the controller is connected to the negative DC bus of each photovoltaic string, the output terminal of the controller is connected to the cathode of the anti-reverse current diode, and the anode of the anti-reverse current diode is connected to the PV negative terminal of the inverter.

[0006] Preferably, the number of anti-reverse current diodes corresponds to the number of photovoltaic strings. The negative DC bus of each photovoltaic string is connected to the cathode of each anti-reverse current diode via a controller, and the anode of each anti-reverse current diode is connected to several PV negative terminals of the inverter.

[0007] Preferably, the voltage of the anti-reverse current diode is greater than the maximum system voltage of the inverter, and the current of the anti-reverse current diode is greater than the maximum current of the photovoltaic string.

[0008] Preferably, the anti-reverse current diode is provided with a heat sink, which is used to dissipate heat from the anti-reverse current diode itself.

[0009] Preferably, a high-voltage fuse is included, one end of which is connected to the anode of the anti-reverse current diode, and the other end of which is connected to the negative PV port of the inverter.

[0010] Preferably, the controller includes a carrier unit, a magnetic ring, and a power supply unit. The output terminal of the carrier unit is connected to the magnetic ring, which is located inside the controller. The negative DC bus of each photovoltaic string passes through the magnetic ring to realize the carrier communication connection between the carrier unit and each MLPE device in the photovoltaic string. The power supply unit supplies power to the carrier unit.

[0011] Preferably, the magnetic ring is disposed inside the controller and located at the far end of the power supply unit.

[0012] Preferably, the controller includes an air switch connected in series on the negative DC bus of each photovoltaic string.

[0013] Preferably, the controller further includes a communication unit, which is connected to a carrier unit and a cloud platform, and a power supply unit supplies power to the communication unit.

[0014] The beneficial technical effects of this utility model include at least the following:

[0015] 1. The anti-reverse current system using photovoltaic module-level power electronic equipment breaks through the conventional thinking that "diodes are only used for bypass protection." It repositions the anti-reverse current diode as an active control element for energy interaction between strings. Creatively, anti-reverse current diodes are connected in parallel in the same direction between different photovoltaic strings under the same MPPT on the DC side. At this time, because the anti-reverse current diodes reverse the current direction and cut off the return path, the low-voltage photovoltaic strings will not generate reverse current, thus avoiding the impact on the MLPE equipment at the module end. This solves the reverse current problem caused by voltage difference in the existing technology, rather than simply transplanting the existing diode application. It ensures the stable operation of the MLPE equipment and improves the stability and reliability of the photovoltaic system.

[0016] 2. Even if the diode completely blocks the reverse current, noise in the carrier communication signal link may still cause the system to malfunction. Specifically, once the carrier signal is unstable, the MLPE device at the module end will repeatedly turn on and off, causing the bus voltage of the entire string to fluctuate continuously, affecting the stability of the entire system. To address this, the controller in this application adopts an integrated design, integrating all functional units inside, and also integrating the magnetic ring into the controller. By directly shortening the communication distance between the magnetic ring and the controller, the coupling communication capability of the magnetic ring is increased, thereby enhancing the stability of the MLPE control signal. This helps the MLPE control signal to accurately identify the reverse current source and only shut down the faulty photovoltaic string, thus improving the system reliability.

[0017] Other features and advantages of this utility model will be disclosed in detail in the following specific embodiments and accompanying drawings. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings:

[0019] Figure 1 This is a schematic diagram of the anti-backflow system structure of the photovoltaic module-level power electronic equipment according to Embodiment 1 of this utility model.

[0020] Figure 2 This is a schematic diagram of the anti-backflow system structure of the photovoltaic module-level power electronic equipment according to Embodiment 2 of this utility model.

[0021] Figure 3 This is a schematic diagram of the internal structure of the controller in Embodiment 2 of this utility model. Detailed Implementation

[0022] The technical solutions of the present utility model will be explained and described below with reference to the accompanying drawings. However, the following embodiments are only preferred embodiments of the present utility model and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present utility model.

[0023] In the following description, terms such as “inner,” “outer,” “upper,” “lower,” “left,” and “right” are used only to facilitate the description of the embodiments and simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0024] Example 1:

[0025] Please see the appendix Figure 1 , Figure 1 A schematic diagram of the backflow prevention system structure of a photovoltaic module-level power electronic device provided in one embodiment of this specification is shown.

[0026] like Figure 1 As shown, the anti-backflow system of the photovoltaic module-level power electronic device can include at least a controller and an anti-reverse current diode. The input terminal of the controller is connected to the negative DC bus of each photovoltaic string, the output terminal of the controller is connected to the cathode of the anti-reverse current diode, the anode of the anti-reverse current diode is connected to the PV negative terminal of the inverter, and the PV positive terminal of the inverter is connected to the positive DC bus of each photovoltaic string.

[0027] Specifically, in this embodiment, the number of anti-reverse current diodes corresponds to the number of photovoltaic strings. The negative DC bus of each photovoltaic string is connected to each anti-reverse current diode (as shown in the attached diagram) via a controller. Figure 1 The cathodes of D1 and D2 in the inverter are connected, and the anodes of each anti-reverse current diode are connected to several PV negative terminals of the inverter.

[0028] like Figure 1 As shown, taking a photovoltaic system comprising two sets of photovoltaic strings connected in parallel to one MPPT of the inverter as an example, each photovoltaic module in each photovoltaic string is connected to an MLPE device (such as a shutdown device or optimizer). The MLPE devices are connected in series. The positive DC bus of the PV1 set of photovoltaic strings is connected to the positive port of the inverter's PV1. The negative DC bus of this set of photovoltaic strings is first connected to the PV1-IN port of the controller, and then comes out through the PV1-OUT port of the controller to the cathode of the anti-reverse current diode D1. Then the anode of the anti-reverse current diode D1 is connected to the negative port of the inverter's PV1. The PV2 set of photovoltaic strings is connected in the same way. It can be seen that in this embodiment, the anti-reverse current diodes are set in parallel in the same direction between different photovoltaic strings under the same MPPT on the DC side.

[0029] Understandably, in existing photovoltaic systems, diodes are mostly used for bypass protection, such as being connected in reverse parallel across the cell string of a single photovoltaic module in bypass mode, or to prevent reverse current from the grid (AC side). This embodiment breaks away from the conventional thinking that "diodes are only used for bypass protection," repositioning the anti-reverse current diode as an active control element for energy interaction between strings. It creatively sets up anti-reverse current diodes in parallel in the same direction between different photovoltaic strings under the same MPPT on the DC side to solve the reverse current problem caused by voltage differences in existing technologies, rather than simply transplanting existing diode applications. This ensures the stable operation of the MLPE equipment, thereby improving the stability and reliability of the photovoltaic system. Specifically:

[0030] When the photovoltaic string is generating electricity normally, the current is input from the positive DC bus of the photovoltaic string to the positive port of PV1 of the inverter, and then flows back to each photovoltaic module from the negative port of PV1 of the inverter through the negative DC bus of the photovoltaic string, forming a complete return path;

[0031] Inside the inverter, two sets of photovoltaic (PV) strings under the same MPPT are connected in parallel. When the inverter's DC terminal is closed, the two PV strings are directly connected in parallel. If the voltage of PV1 is 700V (high voltage) and the voltage of PV2 is 500V (low voltage), then the high-voltage PV string will cause reverse current to flow into the low-voltage PV string. The reverse current path is from the positive DC bus of the high-voltage PV string to the positive DC bus of the low-voltage PV string. The entire low-voltage PV string becomes resistive, and the current flows from the low-voltage PV string... The positive line of the positive DC bus flows directly to the negative DC bus of the low-voltage photovoltaic string, which is the opposite of the current path during normal power supply. At this time, none of the MLPE devices installed on the low-voltage photovoltaic string are powered on, which will cause the reverse current flowing into the string to impact the components of the MLPE devices and increase the risk of device failure. When the inverter DC terminal is turned on, the inverter will adjust. However, similarly, if the voltage difference between the two photovoltaic strings is large, the above reverse current path will also be formed, impacting the MLPE devices of the low-voltage photovoltaic string.

[0032] When backflow occurs, the current path is that the positive line of the positive DC bus of the low-voltage photovoltaic string flows directly to the negative DC bus of the low-voltage photovoltaic string (i.e., from the positive terminal of the high-voltage string → the positive terminal of the low-voltage string → through the module → the negative terminal of the low-voltage string). Traditional bypass diodes (i.e., the path from the positive terminal of the module → the bypass diode → the negative terminal of the module) cannot block this path at all, because they are only used for bypass protection of the battery strings inside the module. However, in this embodiment, anti-reverse current diodes are set in parallel in the same direction between different photovoltaic strings under the same MPPT on the DC side. At this time, because the anti-reverse current diodes reverse the current direction, the return path is cut off, so that the low-voltage photovoltaic string will not generate backflow, thereby avoiding the impact on the MLPE equipment at the module end.

[0033] Specifically, in this embodiment, the voltage of the anti-reverse current diode is greater than the maximum system voltage of the inverter, and the current of the anti-reverse current diode is greater than the maximum current of the photovoltaic string.

[0034] Understandably, the voltage of the anti-reverse diode must meet the voltage requirements of the inverter string system. For example, if the maximum system voltage of the inverter is 1500V, then the reverse voltage of the anti-reverse diode must be greater than 1500V, and 2000V is generally used. The current of the anti-reverse diode needs to be determined based on the maximum current of the photovoltaic string and the heat generation of the anti-reverse diode itself. For example, if the photovoltaic string current is 20A, the current of the anti-reverse diode must be more than 1.5 times that, which is more than 30A.

[0035] Furthermore, in this embodiment, the anti-reverse current diode is equipped with a heat sink (not shown in the figure), which is used to dissipate heat from the anti-reverse current diode itself.

[0036] In this embodiment, the heat sink includes, but is not limited to, thermally conductive materials such as heat-dissipating aluminum blocks, heat pipes, heat spreaders, and other miniature thermally conductive devices. This embodiment does not limit these features.

[0037] It is understandable that the additional power loss caused by reverse current will accumulate heat, and insufficient heat dissipation over a long period of time will have an adverse effect on the characteristics of the reverse current protection diode.

[0038] Furthermore, in this embodiment, a high-voltage fuse (such as...) is included. Figure 2 (F1 and F2 in the diagram), one end of the high-voltage fuse is connected to the anode of the anti-reverse current diode, and the other end of the high-voltage fuse is connected to the negative PV port of the inverter.

[0039] In this embodiment, the voltage of the selected high-voltage fuse is greater than the maximum system voltage of the inverter, and the current of the high-voltage fuse is greater than the maximum current of the photovoltaic string.

[0040] In this embodiment, in addition to the anti-reverse current diode, a DC high-voltage fuse is also configured. The high-voltage fuse has a voltage rating greater than the string voltage, typically 1500V, and a current rating greater than the string's maximum short-circuit current, with a certain margin reserved. For example, if the maximum string current is typically 20A, then a 30A high-voltage fuse is used. The high-voltage fuse can promptly disconnect the photovoltaic string current when there is a momentary sudden change exceeding 30A, thereby avoiding serious interference to the AC power grid.

[0041] Example 2:

[0042] This embodiment provides an anti-backflow system for photovoltaic module-level power electronic equipment. The structure of the anti-backflow system for photovoltaic module-level power electronic equipment provided in Embodiment 1 has been partially improved. Therefore, this embodiment only describes the differences from Embodiment 1. Other parts not described can be referred to the content in Embodiment 1. This embodiment will not repeat them here.

[0043] Anti-reverse current diodes block the reverse current path between strings through their unidirectional conduction characteristics, but they can only solve the current direction problem and cannot deal with the following derivative problems:

[0044] 1. High-frequency harmonic interference: The reverse current may contain harmonic components of the inverter switching frequency (such as above 20kHz), which the diode cannot filter out.

[0045] 2. Risk of signal distortion: Harmonics can couple to control communication signals (such as current sampling or shutdown commands) through the line, causing misjudgment or delay (e.g., false shutdown or delayed response).

[0046] It is understandable that even if the diode completely blocks the reverse current, noise in the carrier communication signal link may still cause the system to malfunction. Specifically, once the carrier signal is unstable, it will cause the MLPE device at the component end to repeatedly turn on and off, causing the voltage of the entire string bus to jump continuously, affecting the stability of the entire system.

[0047] Therefore, in this embodiment, please refer to the appendix. Figure 2 and attached Figure 3 The controller includes a carrier unit, a magnetic ring, and a power supply unit. The output of the carrier unit is connected to the magnetic ring, which is located inside the controller. The negative DC bus of each photovoltaic string passes through the magnetic ring to realize the carrier communication connection between the carrier unit and each MLPE device in the photovoltaic string. The power supply unit supplies power to the carrier unit.

[0048] In this embodiment, the carrier unit is mainly used to communicate with the MLPE device at the photovoltaic module end, and adopts the magnetic ring coupling signal method. The carrier unit needs to have strong stability to ensure stable communication with the MLPE and avoid accidental triggering of the shutdown mechanism.

[0049] In this example, the magnetic ring is integrated into the controller, which directly shortens the communication distance and increases the magnetic ring coupling communication capability, thereby enhancing the stability of the MLPE control signal. This helps the control signal to accurately identify the backflow source and shut down only the faulty photovoltaic string, thus improving the system reliability.

[0050] Furthermore, in this embodiment, the magnetic ring is disposed inside the controller and located at the far end of the power supply unit to achieve interference isolation between the magnetic ring and the power supply module inside the controller.

[0051] Furthermore, in this embodiment, the controller includes an air switch (not shown in the figure), which is connected in series on the negative DC bus of each photovoltaic string.

[0052] Among them, the air switch (also called an air circuit breaker, abbreviated as ACB or MCB) is an automatic protection switch that uses air as the arc extinguishing medium. In this embodiment, its core function is to quickly cut off the fault current with high breaking capacity and protect the downstream equipment from electrical damage.

[0053] Breaking capacity (Icu) refers to the maximum fault current that a circuit breaker can safely interrupt. For example, on the photovoltaic DC side, a high breaking capacity model with Icu≥20kA can be selected (such as the DC circuit breaker model HVDC-63A / 20kA).

[0054] Understandably, in the backflow prevention system, the air switch works in conjunction with the anti-reverse current diode and MLPE device. When backflow occurs between strings, if the diode fails to completely block it, the air switch can cut off the circuit to prevent the reverse current surge from damaging the MLPE device, while also protecting other functional units in the controller from electrical damage.

[0055] Furthermore, in this embodiment, the controller also includes a communication unit, which is connected to a carrier unit and communicates with an existing cloud platform (or remote server) to collect and transmit data. The power supply unit provides power to the communication unit.

[0056] The controller in this embodiment adopts an integrated design, which integrates all functional units inside. At the same time, the magnetic ring is placed inside the control box, which reduces the communication distance between the magnetic ring and the controller and avoids communication instability caused by the distance of the magnetic ring line and external environmental interference of the carrier signal.

[0057] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Those skilled in the art should understand that this utility model includes, but is not limited to, the content described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of this utility model will be included within the scope of the claims.

Claims

1. A backflow prevention system for photovoltaic module-level power electronic equipment, applied to a photovoltaic system comprising several photovoltaic strings and an inverter, characterized in that, It includes a controller and an anti-reverse current diode. The input terminal of the controller is connected to the negative DC bus of each photovoltaic string, the output terminal of the controller is connected to the cathode of the anti-reverse current diode, and the anode of the anti-reverse current diode is connected to the PV negative terminal of the inverter.

2. The backflow prevention system for photovoltaic module-level power electronic equipment as described in claim 1, characterized in that, The number of anti-reverse current diodes corresponds to the number of photovoltaic strings. The negative DC bus of each photovoltaic string is connected to the cathode of each anti-reverse current diode via the controller. The anode of each anti-reverse current diode is connected to several PV negative terminals of the inverter.

3. The backflow prevention system for photovoltaic module-level power electronic equipment as described in claim 2, characterized in that, The voltage of the anti-reverse current diode is greater than the maximum system voltage of the inverter, and the current of the anti-reverse current diode is greater than the maximum current of the photovoltaic string.

4. The backflow prevention system for photovoltaic module-level power electronic equipment as described in claim 2, characterized in that, The anti-reverse current diode is equipped with a heat sink, which is used to dissipate heat from the anti-reverse current diode itself.

5. The backflow prevention system for photovoltaic module-level power electronic equipment as described in claim 1, characterized in that, It includes a high-voltage fuse, one end of which is connected to the anode of the anti-reverse current diode, and the other end of which is connected to the negative PV port of the inverter.

6. The backflow prevention system for photovoltaic module-level power electronic equipment as described in claim 1, characterized in that, The controller includes a carrier unit, a magnetic ring, and a power supply unit. The output terminal of the carrier unit is connected to the magnetic ring, which is located inside the controller. The negative DC bus of each photovoltaic string passes through the magnetic ring to realize the carrier communication connection between the carrier unit and each MLPE device in the photovoltaic string. The power supply unit supplies power to the carrier unit.

7. The backflow prevention system for photovoltaic module-level power electronic equipment as described in claim 6, characterized in that, The magnetic ring is located inside the controller and at the far end of the power supply unit.

8. The backflow prevention system for photovoltaic module-level power electronic equipment as described in claim 6, characterized in that, The controller includes an air switch connected in series on the negative DC bus of each photovoltaic string.

9. The backflow prevention system for photovoltaic module-level power electronic equipment as described in claim 6, characterized in that, The controller also includes a communication unit, which is connected to a carrier unit and a cloud platform. The power supply unit provides power to the communication unit.

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