Inverter parallel anti-reverse flow control system and photovoltaic inverter

Abstract

The present invention belongs to the technical field of photovoltaic power generation, and provides an inverter parallel anti-backflow control system and a photovoltaic inverter, which includes: multiple inverters are arranged in parallel, their power lines are electrically connected to the load, their communication lines are connected to the communication interface of the electric meter, the power interface of the electric meter is electrically connected to the load and the auxiliary power supply respectively, the auxiliary power supply and the inverter jointly provide electrical energy to the load, the auxiliary power supply includes a power grid or a generator, and the system is equipped with an anti-backflow control method. The anti-backflow solution for multiple inverters proposed in the present invention can overcome the disadvantage of the prior art that an additional controller is required to distribute energy. Compared with the anti-backflow solution for a single inverter, it does not require additional cost, is simple and reliable, and effectively realizes the anti-backflow solution under the condition of multiple inverters in parallel.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and in particular to an inverter parallel anti-backflow control system and a photovoltaic inverter. Background Art

[0002] Photovoltaic power is converted into AC power by an inverter for use by local loads, and excess power is fed into the grid. However, when too much power is fed into the grid, not only will the quality of power deteriorate, but it may also exceed the load capacity of the line and cause line failure. In order to prevent these problems, it is necessary to limit the output power of the inverter when necessary.

[0003] Common backflow prevention is for a single inverter. When multiple inverters are jointly protected from backflow, the traditional solution requires an external controller to uniformly control the output power of each inverter to achieve backflow prevention, and the controller will introduce additional costs. Summary of the invention

[0004] The purpose of the present invention is to overcome the complex solution of multiple backflow prevention devices in the prior art that require additional controllers, and to provide a simple and low-cost backflow prevention solution.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] An inverter parallel anti-backflow control system, multiple inverters are arranged in parallel, their power lines are electrically connected to the load, their communication lines are connected to the communication interface of the electric meter, the power interface of the electric meter is electrically connected to the load and the auxiliary power supply respectively, the auxiliary power supply and the inverter jointly provide electric energy for the load, the auxiliary power supply includes a power grid or a generator; the system can implement an anti-backflow control method, the anti-backflow control method includes the steps of:

[0007] Any inverter sends an instruction to the electric meter to obtain first power data currently flowing through the electric meter;

[0008] The electric meter sends first power data currently flowing through the electric meter to all inverters;

[0009] Based on the first power data currently flowing through the electric meter, it is determined whether the inverter has reverse current; and when it is determined that reverse current has occurred, the output power of each inverter that needs to be reduced is determined based on the actual number of equivalent parallel inverters and the first power data currently flowing through the electric meter.

[0010] Furthermore, when the power interface of the electric meter is connected to the power grid, it is determined that output power flows from the inverter to the power grid via the electric meter based on the first power data currently flowing through the electric meter, and reverse flow occurs in the inverter.

[0011] Furthermore, when the power interface of the electric meter is connected to the generator, it is determined whether the first power data currently flowing through the electric meter is the preset target power input by the generator. If not, it is determined that reverse flow occurs in the inverter.

[0012] Furthermore, a switch is provided between the load and the electric meter to close or open the auxiliary power supply to transmit electric energy to the load.

[0013] Furthermore, there are two electric meters arranged in parallel, a power interface of the first electric meter is electrically connected to the power grid, and a power interface of the second electric meter is electrically connected to the generator; the generator and the power grid jointly provide electrical energy to the load.

[0014] Furthermore, a first switch is provided between the load and the first electric meter, and a second switch is provided between the load and the second electric meter, and an auxiliary power supply for providing electric energy to the load is switched by the first switch and the second switch.

[0015] Furthermore, the anti-backflow control method further comprises the steps of:

[0016] After the reverse flow occurs and the output power of each inverter is adjusted, any inverter sends an instruction to the electric meter to obtain the second power data currently flowing through the electric meter;

[0017] If it is determined that the inverter output power needs to be further adjusted based on the second power data currently flowing through the electric meter, the actual number of equivalent parallel inverters is updated, and the output power of each inverter is adjusted based on the updated actual number of equivalent parallel inverters and the second power data.

[0018] Further, the actual number of equivalent parallel inverters is updated according to the first power data and the second power data; the formula for obtaining the updated actual number of equivalent parallel inverters is:

[0019] Ne' = Ne * (P1-P2) / P1;

[0020] Wherein, Ne' represents the actual number of equivalent parallel inverters after updating, P1 represents the first power data, Ne represents the actual number of equivalent parallel inverters before updating, and P2 represents the second power data.

[0021] Furthermore, the actual number of equivalent parallel inverters is corrected based on the Ne' and the Ne, and the correction result is (Ne'+ Ne) / 2.

[0022] The present invention also provides a photovoltaic inverter, which includes a processor, a memory, and a computer program stored in the memory and capable of running on the processor, and the computer program implements the steps of the above-mentioned anti-backflow control method when executed by the processor.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] (1) The anti-backflow solution for multiple inverters proposed in the present invention can overcome the disadvantage of the prior art that an additional controller is required to distribute energy. Compared with the anti-backflow solution for a single inverter, it does not require additional costs, is simple and reliable, and effectively realizes the anti-backflow solution when multiple inverters are connected in parallel;

[0025] (2) The power that needs to be adjusted for each inverter each time is adjusted by the actual number of equivalent parallel inverters, so as to obtain an ideal zero reverse current condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 1 is a schematic diagram of a framework of an inverter parallel anti-backflow system provided in an embodiment of the present invention;

[0028] Figure 2 is a schematic diagram of a system framework when an electric meter provided by an embodiment of the present invention is connected to a power grid;

[0029] Figure 3 is a schematic diagram of the system structure when the electric meter provided by the embodiment of the present invention is connected to the generator;

[0030] Figure 4 is a schematic diagram of the system structure when the electric meter provided by the embodiment of the present invention is connected to the generator;

[0031] Figure 5 It is a flow chart of the anti-backflow control method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0033] In addition, in the present invention, descriptions such as "first", "second", "one", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0034] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0036] The following are specific embodiments of the present invention, and the technical solutions of the present invention are further described in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments.

[0037] First embodiment:

[0038] like Figure 1 As shown, this embodiment provides an inverter parallel anti-backflow system, which includes multiple inverters arranged in parallel, wherein inverter 1, inverter 2 to inverter n are connected in parallel through power lines, connected to the load, and then connected to the electric meter through a switch, and the communication interfaces of inverter 1, inverter 2 to inverter n are connected to form a bus and connected to the communication interface of the electric meter. The power interface of the electric meter is electrically connected to the load and the auxiliary power supply respectively, and the auxiliary power supply and the inverter jointly provide electric energy for the load, and the auxiliary power supply includes but is not limited to the power grid and the generator.

[0039] like Figure 2 As shown, when the electric meter is connected to the grid, inverter 1, inverter 2 to inverter n are connected in parallel through power lines, connected to the load, and then connected to the grid through switch S1 and electric meter 1.

[0040] like Figure 3 As shown, when the electric meter is connected to the generator, inverter 1, inverter 2 to inverter n are connected in parallel through power lines, connected to the load, and then connected to the generator through switch S2 and electric meter 2.

[0041] like Figure 4 As shown, when the grid and the generator are both connected, it is a combination of the above two situations, and the current operation mode is switched by switches S1 and S2, that is, connecting to the grid or connecting to the generator for backflow prevention.

[0042] When the power grid is normal, S1 is closed, S2 is disconnected, and the generator does not work. At this time, it works in the power grid reverse flow prevention state. When the power grid fails, S1 is disconnected, S2 is closed, and the generator starts to work and performs reverse flow prevention work according to the generator mode.

[0043] The anti-backflow solution for multiple inverters proposed in this application reduces the practical use of additional controllers. Compared with the anti-backflow solution for a single inverter, it does not require additional costs, is simple and reliable, and effectively realizes the anti-backflow solution under the condition of multiple inverters in parallel.

[0044] Among them, the system is equipped with a backflow prevention control method, such as Figure 5 As shown, it includes the steps of:

[0045] S1. Any inverter sends an instruction to the electric meter to obtain first power data currently flowing through the electric meter;

[0046] S2, the electric meter sends the first power data currently flowing through the electric meter to all inverters;

[0047] S3. Determine whether reverse current occurs in the inverter based on the first power data currently flowing through the electric meter; and when reverse current occurs, determine the output power that needs to be reduced for each inverter based on the actual number of equivalent parallel inverters and the first power data currently flowing through the electric meter.

[0048] In actual applications, one of the n inverters can be set as the host, and the other inverters can communicate as slaves. The host (taking inverter 1 as an example) first sends a meter reading instruction to the meter, and meter 1 feeds back the power currently flowing through the meter, so that all inverters receive the power data P1, and then determine whether the inverter has reverse flow based on the power data P1.

[0049] It should be noted that when connected to the grid and to the generator respectively, the methods for judging whether reverse flow occurs are different due to the different target output powers.

[0050] When connected to the grid, if the power flowing from the grid to the electric meter is defined as a positive value, when it is judged that output power flows from the inverter to the grid via the electric meter according to the first power data P1 currently flowing through the electric meter, that is, P1<0, it is determined that reverse flow occurs in the inverter.

[0051] When the meter is connected to the generator, in order to make the generator work at the best efficiency point, it is often necessary to make the generator work under certain load conditions. If the power flowing from the generator to the meter is defined as a positive value, compared with the grid backflow prevention, P1=0 needs to be maintained. When the generator is backflow-proof, the first power data P1=Pgen needs to be maintained, and Pgen is the best efficiency point output power of the generator.

[0052] Therefore, when the power interface of the electric meter is connected to the generator, it is necessary to determine whether the first power data P1 currently flowing through the electric meter is the preset target power input by the generator. If not, it is determined that the inverter has reverse flow.

[0053] When it is determined that inversion has occurred, the output power of the inverter needs to be adjusted in time. Therefore, the present application proposes to determine the output power that needs to be reduced for each inverter based on the actual number of equivalent parallel inverters and the first power data P1 currently flowing through the electric meter. At this time, the power that needs to be reduced by each inverter is calculated by default as P1 / Ne, where Ne is the actual number of equivalent parallel inverters, and its initial value is the number of parallel inverters n.

[0054] Since the input power of the photovoltaic inverter is affected by the photovoltaic panels or the actual number of working units, one adjustment cannot achieve the ideal zero reverse current situation, so it is necessary to further adjust the output power of each inverter.

[0055] When the host sends a meter reading command to the meter next time, all inverters receive the updated second power data P2. If P2<0 (or P2<Pgen), there is still reverse flow; if P2>0 (or P2>Pgen), it means that the power reduction is too much.

[0056] It is determined that the inverter output power needs to be further adjusted, so that the actual equivalent parallel inverter number Ne is updated, and the output power of each inverter is adjusted according to the updated actual equivalent parallel inverter number Ne' and the second power data P2.

[0057] The formula for obtaining the updated actual equivalent parallel inverter quantity is:

[0058] Ne' = Ne * (P1-P2) / P1;

[0059] Among them, Ne' represents the actual number of equivalent parallel inverters after the update, P1 represents the first power data, Ne represents the actual number of equivalent parallel inverters before the update, and P2 represents the second power data; this adjustment allocates power according to Ne', and the power that needs to be adjusted for each inverter is P2 / Ne'. It should be made clear that power detection and command sending are continuous, P1 as the first power represents the power of the previous detection, and P2 as the second power is the power currently detected.

[0060] For example, in the embodiment where only the grid is used as the auxiliary power source, there are 10 inverters with an overcurrent of 88kw. According to the first adjustment, each inverter needs to reduce the current by 8.8kw. However, in practice, there are 2 inverters running at 0 power, 3 inverters running at 8kw, and 5 inverters running at 12.8kw.

[0061] After one adjustment, 5 inverters run at 0 power and 5 inverters run at 4kw power. At this time, there is still an overcurrent of 4×5=20kw; at this time, Ne'=10×(-88+20 / -88)=8.5 inverters

[0062] The second adjustment, Ne is 8.5 units, the overcurrent is 20kw, each inverter needs to reduce the current by 2.352kw, at this time there is still (4-2.352)×5=8.235kw overcurrent; at this time Ne'=8.5×(-20+8.235 / -20)=4.999 units

[0063] The third adjustment, Ne is 4.999 units, the overcurrent is 8.235kw, each inverter needs to reduce the current by 1.648kw, 1.648+2.352=4kw, and the current reduction is completed.

[0064] By introducing a current reduction strategy based on the number of equivalent parallel inverters, it is no longer necessary to adjust the working state of a single inverter separately. The current reduction effect can be achieved by simultaneously adjusting the current reduction values ​​of all inverters.

[0065] Second embodiment:

[0066] In order to prevent Ne from jumping due to errors, its value should be filtered in actual applications, and the actual number of equivalent parallel inverters is corrected based on Ne' and Ne. The correction result is (Ne'+ Ne) / 2. The error threshold can be set to confirm whether to make a correction. For example, the error threshold is 40%. When the relative error is greater than the error threshold, correction is made. For example, Ne is 10, Ne' is 5, and the relative error is (10-5) / 10=50%>40%. The output Ne' is adjusted to (10+5) / 2=7.5 output. In other embodiments, the error threshold can take other values, and there is no limitation on this.

[0067] The anti-backflow solution for multiple inverters proposed in this application adjusts the power that needs to be adjusted for each inverter each time by actually using the number of equivalent parallel inverters, thereby achieving an ideal zero backflow situation.

[0068] This embodiment also provides a photovoltaic inverter, which includes a processor, a memory, and a computer program stored in the memory and capable of running on the processor. When the computer program is executed by the processor, the steps of the above-mentioned anti-backflow control method are implemented.

[0069] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. An inverter parallel anti-backflow control system, characterized in that: A plurality of inverters are arranged in parallel, the power lines of which are electrically connected to the load, the communication lines of which are connected to the communication interface of the electric meter, the power interface of the electric meter is electrically connected to the load and the auxiliary power supply respectively, the auxiliary power supply and the inverter jointly provide electric energy for the load, the auxiliary power supply includes a power grid or a generator; the system can implement an anti-backflow control method, the anti-backflow control method includes the steps of: Any inverter sends an instruction to the electric meter to obtain first power data currently flowing through the electric meter; The electric meter sends first power data currently flowing through the electric meter to all inverters; Determining whether reverse current occurs in the inverter based on first power data currently flowing through the electric meter; and when it is determined that reverse flow occurs, determining the output power of each inverter that needs to be reduced based on the actual number of equivalent parallel inverters and the first power data currently flowing through the electric meter; After the reverse flow occurs and the output power of each inverter is adjusted, any inverter sends an instruction to the electric meter to obtain the second power data currently flowing through the electric meter; If it is determined that the inverter output power needs to be further adjusted according to the second power data currently flowing through the electric meter, the actual number of equivalent parallel inverters is updated, and the output power of each inverter is adjusted according to the updated actual number of equivalent parallel inverters and the second power data; The actual equivalent parallel inverter quantity is updated according to the first power data and the second power data.

2. The inverter parallel anti-backflow control system according to claim 1, characterized in that: When the power interface of the electric meter is connected to the power grid, it is determined that output power flows from the inverter to the power grid via the electric meter according to first power data currently flowing through the electric meter, and reverse flow occurs in the inverter.

3. The inverter parallel anti-backflow control system according to claim 1, characterized in that: When the power interface of the electric meter is connected to the generator, it is determined whether the first power data currently flowing through the electric meter is the preset target power input by the generator. If not, it is determined that the inverter has reverse flow.

4. The inverter parallel anti-backflow control system according to claim 1, characterized in that: A switch is provided between the load and the electric meter to close or open the auxiliary power supply to transmit electric energy to the load.

5. The inverter parallel anti-backflow control system according to claim 1, characterized in that: There are two electric meters arranged in parallel, a power interface of the first electric meter is electrically connected to the power grid, and a power interface of the second electric meter is electrically connected to the generator; the generator and the power grid jointly provide electrical energy for the load.

6. The inverter parallel anti-backflow control system according to claim 5, characterized in that: A first switch is provided between the load and the first electric meter, and a second switch is provided between the load and the second electric meter. The first switch and the second switch are used to switch an auxiliary power supply for providing electric energy to the load.

7. The inverter parallel anti-backflow control system according to claim 1, characterized in that: The updated formula for the actual equivalent number of parallel inverters is: Ne' = Ne * (P1-P2) / P1; Wherein, Ne' represents the actual number of equivalent parallel inverters after updating, P1 represents the first power data, Ne represents the actual number of equivalent parallel inverters before updating, and P2 represents the second power data.

8. The inverter parallel anti-backflow control system according to claim 7, characterized in that: The actual number of equivalent parallel inverters is corrected based on the Ne' and the Ne, and the correction result is (Ne'+ Ne) / 2.

9. A photovoltaic inverter, characterized in that: The method comprises a processor, a memory and a computer program stored in the memory and capable of running on the processor, wherein the computer program, when executed by the processor, implements the steps of the anti-backflow control method according to any one of claims 1 to 8.

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