Distributed photovoltaic power generation anti-reflux device

Abstract

The utility model discloses a distributed photovoltaic power generation anti-reflux device, and relates to the technical field of photovoltaic power generation. Comprising a power grid power source and a load main circuit, the power grid power source is connected with the load main circuit through a power circuit breaker, one side of the load main circuit is connected with an alternating current combiner box through a first contactor, the alternating current combiner box is connected with an inverter, and the other side of the load main circuit is further provided with a load branch. A load circuit breaker and a fourth current transformer are sequentially mounted on the load branch circuit; and an anti-reflux assembly, a first current transformer, a second contactor, a third current transformer and a compensation branch circuit are further included. According to the utility model, the size of the output power of the anti-countercurrent device system is adjusted through resistance compensation power, reverse power generation is prevented, grid operation of photovoltaic power generation is guaranteed to the greatest extent, and the inverter does not need to change the current output power when the load is relatively small and fluctuates frequently in a short time, so that the cost is reduced. And automatically adjusting the output power of the power generation system to match the current load.

Description

Technical Field

[0001] The utility model relates to the technical field of photovoltaic power generation, and particularly relates to a distributed photovoltaic power generation anti-counterflow device. Background Art

[0002] For traditional anti-counterflow devices, current data is collected at the grid and load demarcation point. When there is a slight fluctuation in the main load path, the grid-connected switch of the photovoltaic power generation system is tripped or the output of the inverter is instantaneously adjusted by means of communication, resulting in frequent switching of the inverter or the branch of the busbar trunking system. The current mutation generated during this period frequently impacts the inverter, reducing the service life of the inverter. Summary of the Utility Model

[0003] In view of the above technical problems, the utility model provides a distributed photovoltaic power generation anti-counterflow device, which is used to solve the problems that when there is a slight fluctuation in the main load path, the grid-connected switch of the photovoltaic power generation system is tripped or the output of the inverter is instantaneously adjusted, and the current mutation generated during this period frequently impacts the inverter, reducing the service life of the inverter.

[0004] In order to achieve the above purpose, the technical solution of the utility model is specifically as follows:

[0005] A distributed photovoltaic power generation anti-counterflow device includes a grid power supply and a main load path. The grid power supply is connected to the main load path through a power circuit breaker. One side of the main load path is connected to an AC busbar trunking system through a first contactor. The AC busbar trunking system is connected to an inverter. The other side of the main load path also branches into a load branch. A load circuit breaker and a fourth current transformer are sequentially installed on the load branch. The device also includes an anti-counterflow component, a first current transformer, a second contactor, a third current transformer, and a compensation branch;

[0006] The first current transformer is installed between the grid power supply and the power circuit breaker;

[0007] The second contactor is installed between the monitoring point A and the first contactor;

[0008] The third current transformer is installed between the first contactor and the AC busbar trunking system;

[0009] The compensation branch is connected between the second contactor and the first contactor. A switching-off circuit breaker, a second current transformer, and a resistor cabinet are sequentially connected on the compensation branch;

[0010] The first current acquisition terminal of the anti-counterflow component is connected to the third current transformer;

[0011] The grouped switching signal of the anti-counterflow component is connected to the resistor cabinet;

[0012] The third current acquisition terminal of the anti-counterflow component is connected to the second current transformer;

[0013] The opening and closing control signal of the anti-backflow component is connected to the second contactor;

[0014] A fifth current transformer is installed between the monitoring point A and the second contactor, and the fourth current acquisition terminal of the anti-backflow component is connected to the fifth current transformer;

[0015] The voltage acquisition input terminal of the anti-backflow component is connected to point D on the grid power supply;

[0016] The second current acquisition terminal of the anti-backflow component is connected to the first current transformer;

[0017] The voltage acquisition output terminal of the anti-backflow component is connected to point C on the main load circuit;

[0018] The opening and closing control signal of the anti-backflow component is connected to the first contactor.

[0019] Furthermore, the resistor cabinet includes a main contactor group and a plurality of resistor strings. The main contactor group is respectively connected to the grouped switching signal of the anti-backflow component and the second current transformer, and the plurality of resistor strings are respectively connected to the respective sub-contacts of the main contactor group.

[0020] Compared with the prior art, the beneficial effects of the present utility model are:

[0021] First, it avoids the frequent switching of the traditional anti-backflow device to the inverter or the branch of the busbar box during load fluctuations, reduces the impact of current mutation on the inverter, and prolongs the service life of the inverter;

[0022] Second, while ensuring no reverse power generation, it effectively extends the power supply duration of photovoltaic power generation to the load, enables the load to use the photovoltaic system power supply as much as possible, effectively reduces the power generation loss due to load fluctuations, and further improves the self-use power ratio;

[0023] Third, when allowing the load power to fluctuate within a large range (within 95% of the maximum photovoltaic power generation), the photovoltaic system always remains in the on-grid state;

[0024] Fourth, it provides great convenience for small inverters without communication power regulation function to be connected to the grid and ensure maximum power generation efficiency when the surplus power is not fed back to the grid. Brief Description of the Drawings

[0025] Figure 1 It is the connection relationship diagram of the present utility model;

[0026] Figure 2 It is the operation flow chart of the present utility model;

[0027] In the figure:

[0028] 1. Grid power supply; 2. Main load circuit; 3. First contactor; 4. AC busbar box; 5. Inverter; 6. Load branch circuit; 7. Load circuit breaker; 8. Fourth current transformer; 9. Anti-backflow component; 10. First current transformer; 11. Second contactor; 12. Third current transformer; 13. Compensation branch circuit; 14. Power circuit breaker; 15. Switch-on and cut-off circuit breaker; 16. Second current transformer; 17. Resistance cabinet; 18. Main contactor group; 19. Resistance string; 20. Fifth current transformer. Detailed implementation manners

[0029] To make the objectives, technical solutions and advantages of the present utility model clearer, the present utility model will be further described in detail below in combination with the specific implementation manners and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present utility model. In addition, in the following descriptions, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present utility model.

[0030] The system is as Figure 1 shown. First, close the compensation circuit breaker 15 to connect the resistance cabinet 17 to the system. The second contactor 11 is in the off state. Close the first contactor 3 and the voltage acquisition circuit, that is, connect the voltage acquisition circuit (input) and the voltage acquisition (output). Use the grid voltage to pre-charge the inverter and complete the phase matching of the grid voltage and the photovoltaic voltage (completed by the inverter). Close the first group of contactors of the main contactor group 18, and use the first group of contactors of the main contactor group 18 as the test resistance to test whether the photovoltaic power P2 is greater than or equal to 5%P2 MAX , if it is greater than 5%P2 MAX , it is also necessary to satisfy that the grid power P1 (at this time, the grid power P1 = the load power P7) ≥ P2 + set value 1. If the above conditions are not met, it means that the photovoltaic power generation is small or the load power is small, and it is not suitable to start grid connection. Then continue to judge after a short delay; if it is satisfied, it means that both the power generation power and the load meet the requirements. Then disconnect the first group of contactors of the main contactor group 18 and enter the next step of grid connection, and close the second contactor 11.

[0031] After grid connection, it is necessary to disconnect the voltage acquisition output circuit and monitor the magnitude of the system output power P6 at all times. At any moment, when it is monitored that P6 < 0, it means that the system has an abnormal state, that is, the phenomenon that the grid power supply supplies power to the main contactor group 18 occurs. It is necessary to immediately trip the second contactor and cut off all the contactors from the first to the Nth groups of the main contactor group and re-enter the cycle. If P6 < 0 appears again after re-entering the cycle, it is determined that the contactor is stuck and the system alarms and stops; if P6 ≥ 0, there is no action, and after a delay of 0.5 s, continue to monitor, and at the same time continue to judge the magnitude of the grid power P1 at point A.

[0032] Judge whether the grid power P1 at point A is greater than the set value 1 (threshold value), that is, the minimum power grid connection current. If it is greater than the set value 1, it indicates no reverse power. The load power demand at point B is relatively large. The photovoltaic power of the first contactor 3 plus the grid power at point A is equal to the load power at point B, that is, P2 + P1 = P7. At this time, all the contactors in the first to the Nth groups of the main contactor group 18 are in the cut-off state. The photovoltaic power of the first contactor 3 is equal to the output power of the second contactor 11, that is, P2 = P6, and the photovoltaic system is in the full-power generation state.

[0033] After grid connection, when it is judged that the grid power P1 at point A is less than the set value 1 (threshold value), it indicates that reverse power is generated. The load power demand at point B is relatively small. In addition to meeting the load power at point B, the remaining power of the photovoltaic power of the first contactor 3 flows reversely through the grid, making P1 less than the set value 1. Since P7 = P2 + P1 = P6 + P1, under the condition that the load power at point B remains unchanged, reducing the photovoltaic power P2 of the first contactor 3 or reducing the output power P6 of the second contactor 11 can increase the grid power P1 until it is greater than the set value 1.

[0034] This scheme increases the grid power P1 by reducing the output power P6 of the second contactor 11.

[0035] Insert the contactor of the first group of the main contactor group 18. The rated power of the resistor carried by the contactor of the first group is P R1 , after the contactor of the first group is inserted, compensation power P3 is immediately generated in the compensation branch 13, and P3 = P R1 . The output power of the second contactor 11 is reduced from the original P6 = P2 to P6 = P2 - P3, that is, P6 = P2 - P R1 . At this time, judge again whether the grid power P1 at point A is greater than the set value 1 (threshold value). If it is greater than the set value 1 (threshold value), it indicates that the reverse power disappears and the system operation returns to normal.

[0036] After the system returns to normal, if the load power at point B increases, the grid power P1 at point A will also increase accordingly. To ensure that the output power of the system is at the maximum value without reverse power, when the grid power P1 at point A increases to a certain value, this group of contactors needs to be cut off so that the output power changes from P6 = P2 - P R1 to P6 = P2; therefore, detect the grid power P1 at point A. When P1 ≥ the rated power P of the resistor carried by the contactor of the first group of the main contactor group 18 R1 + the set value 1, that is, P1 ≥ P R1 + the set value 1, cut off the contactor of the first group. (However, after cutting off the contactor of the first group of the main contactor 18, it is necessary to consider the possibility that the photovoltaic power P2 may decrease due to other reasons (such as sudden weather changes, etc.). Therefore, it is necessary to judge the truth or falsehood of P2 ≥ 5%P2 MAX . If P2 < 5%P2 MAX, it indicates that the output of the photovoltaic power P2 decreases due to its own reasons to the point where it can no longer generate electricity, and the second contactor needs to be tripped to cut off all contactors in the 1st to Nth groups of the main contactor group 18. If P2 ≥ 5%P2 MAX , then continue to judge the magnitude of the grid power P1 and execute downward. ); When P1 < P R1 + set value 1, maintain the input state of the contactor in the 1st group of the main contactor group 18, and continue to monitor the grid power P1 at point A.

[0037] After the contactor in the 1st group of the main contactor group 18 is input, if the grid power P1 at point A is still less than the set value 1 (threshold value), it indicates that reverse power still exists, and the output power P6 of the second contactor 11 still needs to be further reduced.

[0038] Then input the contactor in the 2nd group of the main contactor group 18. The rated power of the resistor carried by the 2nd group of contactors is P R2 , after the 2nd group of contactors is input, the generated compensation power P3 changes from P3 = P R1 to P3 = P R1 + P R2 , and the output power of the second contactor 11 changes from the original P6 = P2 - P3 = P2 - P R1 to P6 = P2 - P3 = P2 - P R1 - P R2 , at this time, judge again whether the grid power P1 at point A is greater than the set value 1 (threshold value). If it is greater than the set value 1 (threshold value), it indicates that the reverse power disappears and the system operation returns to normal.

[0039] Similarly, if the load power at point B increases at this time, when the grid power P1 at point A ≥ P R2 + set value 1, to ensure that the output power of the system is always at the maximum value without reverse power, it is necessary to timely cut off the contactors in this group, then judge the value of P1, and then if P1 ≥ P R1 + set value 1, then continue to cut off the contactor in the 1st group.

[0040] After the contactor in the 2nd group of the main contactor group 18 is input, if the grid power P1 at point A is still less than the set value 1 (threshold value), it indicates that reverse power still exists, and the output power P6 of the second contactor 11 still needs to be further reduced.

[0041] And so on, input the contactor in the 3rd group, the contactor in the 4th group of the main contactor group 18 until the contactor in the Nth group. The rated powers of the resistors carried by each contactor are P R3 、P R4 、......、P RN-1 、P RN .

[0042] After the contactor in the Nth group of the main contactor group 18 is input, the generated compensation power is:

[0043] P3 = P R1 + P R2 + P R3 + P R4 +......+ P RN-1 + P RN = 95%P2 MAX

[0044] At this time, the load power P7 at B drops to 5% of the photovoltaic power of the first contactor 3. If the grid power P1 at A is still less than the set value 1 (threshold value), then the second contactor 11 is tripped, and all contactors in the 1st to Nth groups of the main contactor group 18 are cut off. At this time, the grid power P1 at A is equal to the load power P7 at B, that is, P1 = P7. The value of the grid power P1 at A is detected. When P1 recovers to be greater than 5% of the photovoltaic power P2 MAX i.e., P1 > 5%P2 MAX + set value 1, the second contactor 11 is closed, and the system is restarted for grid connection, entering cyclic regulation.

[0045] Example: The total power of a certain distributed photovoltaic system is 500 kW, consisting of 5 inverters 5 with a power of 100 kW each. At a certain moment, the photovoltaic system is in the maximum power generation state, and the inverters 5 are running at full load. At this time, the load suddenly changes from 550 kW to 390 kW. If the traditional method is used to cut off the inverters 5, then 2 inverters 5 need to be cut off to avoid reverse power. The remaining 3 inverters 5 work, with a total power of 300 kW, resulting in a loss of 90 kW.

[0046] If the present technical solution is adopted, a resistor cabinet 17 with a power of 500 kW * 0.95 = 475 kW is configured, and 19 groups of contactors are set. Then the resistance power of each group of contactors is 25 kW, that is, P R1 = P R2 = P R3 = P RN = 25 kW. The set value 1 is set to 2 kW. The inverters 5 are running at full load, P2 = 500 kW.

[0047] The load power P7 at A changes suddenly from 550 kW to 390 kW. The anti - reverse current device monitors that the grid power P1 at A changes suddenly from 550 - 500 = 50 kW to 390 - 500 = - 110 kW, P1 = - 110 kW. The set value 1 is set to 2 kW, P1 < set value 1, so the contactor in the 1st group of the main contactor group 18 is put into operation. The output power P6 of the second contactor 11 drops from 500 kW to P6 = P2 - P3 = P2 - P R1 = 500 - 25 = 475 kW. At this time, the grid power P1 at A = P7 - P6 = 390 - 475 = - 85 kW.

[0048] Judge that the grid power P1 at point A is still less than the set value 1, continue to switch on the second group of contactors in the main contactor group 18, and the compensation power P3 = P R1 +P R2 = 50, the output power P6 of the second contactor 11 is P6 = P2 - P3 = 500 - 50 = 450 kW, and the grid power P1 at point A is P1 = P7 - P6 = 390 - 450 = -60 kW.

[0049] Judge that the grid power P1 at point A is still less than the set value 1, continue to switch on the third group of contactors in the main contactor group 18, and the compensation power P3 = P R1 +P R2 +P R3 = 75, the output power P6 of the second contactor 11 is P6 = P2 - P3 = 500 - 75 = 425 kW, and the grid power P1 at point A is P1 = P7 - P6 = 390 - 425 = -35 kW.

[0050] Judge that the grid power P1 at point A is still less than the set value 1, continue to switch on the fourth group of contactors in the main contactor group 18, and the compensation power P3 = P R1 +P R2 +P R3 +P R4 = 100, the output power P6 of the second contactor 11 is P6 = P2 - P3 = 500 - 100 = 400 kW, and the grid power P1 at point A is P1 = P7 - P6 = 390 - 400 = -10 kW.

[0051] Judge that the grid power P1 at point A is still less than the set value 1, continue to switch on the fifth group of contactors in the main contactor group 18, and the compensation power P3 = P R1 +P R2 +P R3 +P R4 +P R5 = 125 kW, the output power P6 of the second contactor 11 is P6 = P2 - P3 = 500 - 125 = 375 kW, and the grid power P1 at point A is P1 = P7 - P6 = 390 - 375 = 15 kW.

[0052] Judge that the grid power P1 at point A is greater than the set value 1, and continue to judge the magnitude relationship between P1 and P R5 + the set value 1. P1 = 15 kW, P R5 = 25 kW, the set value 1 = 2 kW, P1 < P R5 + the set value 1, and maintain the current state.

[0053] At this time, the output power P6 of the entire system is P6 = P2 - P3 = 500 - 125 = 375 kW, which is 75 kW more than that of the traditional direct inverter cut-off method 5.

[0054] If in the next moment, the load power P7 at point B increases from 390 kW to 443 kW, then the grid power P1 at point A increases from P1 = P7 - P6 = 390 - 375 = 15 kW to P1 = P7 - P6 = 443 - 375 = 68 kW, and P1 ≥ P R5 + Set value 1, cut off the contactors of the main contactor group 18 of this group (the 5th group). After cutting off, the compensation power P3 = P R1 + P R2 + P R3 + P R4 = 100 kW, the output power P6 of the second contactor 11 = P2 - P3 = 500 - 100 = 400 kW, and the grid power P1 at point A = P7 - P6 = 443 - 400 = 43 kW;

[0055] Judge P1 ≥ P R4 + Set value 1, continue to cut off the contactors of the 4th group of the main contactor group 18. After cutting off, the compensation power P3 = P R1 + P R2 + P R3 = 75 kW, the output power P6 of the second contactor 11 = P2 - P3 = 500 - 75 = 425 kW, and the grid power P1 at point A = P7 - P6 = 443 - 425 = 18 kW; P1 ≥ set value 1, and P1 < P R3 + Set value 1, maintain the current state, and wait for the grid power P1 at point A to change again, then input or cut off the contactors of the main contactor group 18.

[0056] The illustrated resistor cabinet 17 is only a schematic diagram. In actual application, the resistors in the resistor cabinet 17 can be connected in multiple series - parallel forms. Each group is connected in series with a set of contactors, and is divided into N groups. The larger the value of N, the more precise the adjustment, but the response speed will be slower. The smaller the value of N, the faster the response speed, but the adjustment accuracy will be smaller. Generally, a value around 10 - 30 can be taken. To ensure that when the value of N is large, the system still has a relatively fast response time and the reverse - flow existence time is shortened as much as possible, an acceleration sub - routine can be set in the program. That is, when it is detected that the main contactor group 18 continuously inputs 3 groups of contactors and P1 is still less than the set value 1, start the acceleration sub - routine, that is, directly input 4 / N groups of contactors. If P1 < set value 1, then input 2 / N groups of contactors. If P1 < set value 1, then input all N groups of contactors until P1 ≥ set value 1, and then enter the loop, and use the main program to gradually cut off the over - input contactors to keep P1 within {P1|set value 1 ≤ P1 ≤ P RX + Set value 1, X takes 1, 2, 3... N}, so that the reverse - flow can be eliminated with a maximum of 6 compensations.

[0057] The execution process is as Figure 2 shown. Prepare to start (initial state: the first contactor 3 is in the off state, the compensation circuit breaker 15 is in the off state, and the second contactor 11 is in the off state)

[0058] (I) The anti-backflow component 9 is powered on, and the device is in a normal working state. The compensation circuit breaker 15 is closed, and each air switch above the main contactor group 18 is closed in sequence. After ensuring that once the first contactor 3 is closed, the upper ports of all contactors in the main contactor group 18 are energized, and after the device self-check is normal, an instruction is issued to close the first contactor 3.

[0059] (II) The voltage acquisition circuit is closed, that is, the voltage acquisition circuit (input) and voltage acquisition (output) are connected. The grid voltage is sent to the busbar box 4 (inverter) via the pre-charge circuit of the anti-backflow component 9 to pre-charge the inverter. After the photovoltaic voltage and the grid voltage are phase-matched (completed by the inverter), the first group of contactors in the main contactor group 18 is closed.

[0060] (III) After closing the first group of contactors in the main contactor group 18, a current loop is formed, and the actual magnitude of the photovoltaic power P2 is measured. When P2 > 5%P2 MAX and P1 ≥ P2 + set value 1, it indicates that the sunlight is sufficient, the photovoltaic power reaches the output standard and the load power is appropriate, and proceed to the next step; otherwise, delay for 0.5 seconds (adjustable) and judge again until the condition is met and then proceed to the next step.

[0061] (IV) The test loop is opened, that is, the first group of contactors in the main contactor group 18.

[0062] (V) The second contactor 11 is closed, and the system enters the grid-connected operation state; immediately disconnect the output of the voltage acquisition circuit. And monitor the system output power P6 throughout the process after grid connection. When it is monitored that P6 < 0, it indicates that the system is in an abnormal state. It is not allowed for the grid power supply to supply power to the contactor group 18. Immediately open the second contactor and cut off all contactors in the first to N groups of the main contactor group. Re-enter the loop of (II). If P6 < 0 appears again after re-entering the loop, it is determined that the contactor is stuck and the system alarms and stops; if P6 ≥ 0, there is no action. After a delay of 0.5 s, continue to monitor, and at the same time continue to execute the judgment of the grid power P1 magnitude at point A in (VI).

[0063] (VI) Judge the magnitude of the grid power P1. When P1 ≥ set value 1, it indicates that the load power at point B is large, and the photovoltaic power P2 plus the grid power P1 can meet the load power P7 at point B. The photovoltaic power P2 is fully output via the second contactor 11, and the photovoltaic power P2 = the system output power P6; when P1 ≤ set value 1, it indicates that the load power at point B is small, and the photovoltaic power P2 ≥ the load power P7 at point B. The excess photovoltaic power may form a reverse power by being sent to the grid at point A, which is not allowed.

[0064] (VII) When the reverse power trend is detected (i.e., when P1 < set value 1), the anti-counterflow component 9 immediately enters the compensation state and controls the input of the first group of contactors in the main contactor group 18. After the input, the compensation circuit breaker 15 immediately generates a compensation power P3 = P R1 =U 2 / R1, and the system output power P6 = photovoltaic power P2 - compensation power P3, that is, the excess photovoltaic power is consumed by the compensation power P3 at the compensation circuit breaker 15.

[0065] (VIII) Continue to judge the magnitude of the grid power P1. When P1 ≥ set value 1, it indicates that after the compensation circuit breaker 15 generates the compensation power, the system output power P6 decreases, making the system output power P6 < the load power P7 at point B, and the reverse power disappears.

[0066] However, with the fluctuation of the load, it is possible that the load power P7 at point B increases in the next moment, and the demand for the system output power P6 rises. Then, when the load power P7 at point B increases to a certain value, the first group of contactors in the main contactor group 18 must be disconnected to restore the system output power P6. Therefore, after judging that P1 ≥ set value 1, further continue to judge P1 ≥ P R1 + set value 1. If it is true, it indicates that the increment of the load power P7 at point B of the load reaches the current compensation power P of the system R1 , then disconnect the first group of contactors in the main contactor group 18, and then judge whether it is possible that the photovoltaic power P2 decreases due to other reasons (such as sudden weather changes, etc.), that is, judge the truth or falsehood of P2 ≥ 5%P2 MAX If P2 < 5%P2 MAX , it indicates that the output of the photovoltaic power P2 decreases due to its own reasons to the point where it cannot continue to generate electricity. It is necessary to trip the second contactor, disconnect all the first to N groups of contactors in the main contactor group, and then return to (II) to wait for the output of the photovoltaic power P2 to recover. If P2 ≥ 5%P2 MAX , then return to (VI) to continue judging the magnitude of the grid power P1 and execute downward; if P1 < set value 1 + P R1 , it indicates that the increment of the load power P7 at point B of the load does not reach the current compensation power P of the system R1 , and reverse power will be generated after disconnecting the first group of contactors in the main contactor group 18. Therefore, return to (VIII) to continue judging the magnitude of P1 and execute downward.

[0067] When P1 < set value 1 in this step, it indicates that after the compensation circuit breaker 15 generates the compensation power, the degree of decrease in the system output power P6 is not large, and the system output power P6 is still greater than the load power P7 at point B, and the reverse power has not disappeared. It is necessary to input the second group of contactors in the main contactor group 18.

[0068] (IX) After the anti-counterflow component 9 activates the second group of contactors in the main contactor group 18, after activation, the compensation circuit breaker 15 generates a compensation power P3 = P R1 +P R2 =U 2 / R1 + U 2 / R2.

[0069] (X) After activating the second group of contactors in the main contactor group 18, continue to judge the magnitude of the grid power P1. When P1 ≥ set value 1, it indicates that after the compensation circuit breaker 15 generates compensation power, the system output power P6 decreases, causing the system output power P6 < the load power P7 at point B, and the reverse power disappears. However, with the fluctuation of the load, it is possible that the load power P7 at point B increases in the next moment, and the demand for the system output power P6 rises. Then, it is necessary to disconnect the second group of contactors in the main contactor group 18 when the load power P7 at point B increases to a certain value, thereby restoring the system output power P6. Therefore, after judging P1 ≥ set value 1, further continue to judge P1 ≥ P R2 + set value 1. If it is true, it means that the increment of the load power P7 at point B reaches the current system compensation power P R2 , then disconnect the second group of contactors in the main contactor group 18, and then return to (VIII) to continue judging the magnitude of the grid power P1 and execute downward; if it is false, it means that the increment of the load power P7 at point B does not reach the current system compensation power P R2 , and reverse power will be generated after disconnecting the second group of contactors in the main contactor group 18, so return to (X) to continue judging the magnitude of P1 and execute downward. When P1 < set value 1 in this step, it indicates that after the compensation circuit breaker 15 generates compensation power, the decrease in the system output power P6 is not significant, and the system output power P6 is still greater than the load power P7 at point B, and the reverse power has not disappeared. It is necessary to activate the third group of contactors in the main contactor group 18.

[0070] (XI) After the anti-counterflow component 9 activates the third group of contactors in the main contactor group 18, after activation, the compensation circuit breaker 15 generates a compensation power P3 = P R1 +P R2 +P R3 =U 2 / R1 + U 2 / R2 + U 2 / R3.

[0071] (XII) After the third contactor of the main contactor group 18 is put in, continue to judge the magnitude of the grid power P1. When P1 ≥ set value 1, it indicates that after the compensation circuit breaker 15 generates compensation power, the system output power P6 decreases, making the system output power P6 < the load power P7 at point B, and the reverse power disappears. However, with the fluctuation of the load, it is possible that the load power P7 at point B increases in the next moment, and the demand for the system output power P6 rises. Then, when the load power P7 at point B increases to a certain value, the third contactor of the main contactor group 18 must be cut off to restore the system output power P6. Therefore, after judging that P1 ≥ set value 1, further continue to judge P1 ≥ P R3 + set value 1. If it is true, it indicates that the increment of the load power P7 at point B of the load reaches the compensation power P of the system at this time R3 , then cut off the third contactor of the main contactor group 18, and then return to point (X) to continue judging the magnitude of the grid power P1 and execute downward; if it is false, it indicates that the increment of the load power P7 at point B of the load cannot reach the compensation power P of the system at this time R3 . After cutting off the third contactor of the main contactor group 18, reverse power will be generated. Therefore, return to (XII) to continue judging the magnitude of P1 and execute downward. When P1 < set value 1 in this step, it indicates that after the compensation circuit breaker 15 generates compensation power, the degree of decrease in the system output power P6 is not large, and the system output power P6 is still greater than the load power P7 at point B, and the reverse power has not disappeared. It is necessary to put in the fourth contactor of the main contactor group 18

[0072] (XIII) And so on. When the anti - reverse current component 9 puts in the Nth (the last group) contactor of the main contactor group 18, the compensation circuit breaker 15 generates compensation power P3 = P R1 + P R2 + P R3 +......+ P RN = U 2 / R1 + U 2 / R2 + U 2 / R3 +......+ U 2 / RN

[0073] (XIV) After the Nth contactor of the main contactor group 18 is put in, continue to judge the magnitude of the grid power P1. When P1 ≥ set value 1, it indicates that after the compensation circuit breaker 15 generates compensation power, the system output power P6 decreases, making the system output power P6 < the load power P7 at point B, and the reverse power disappears. However, with the fluctuation of the load, it is possible that the load power P7 at point B increases in the next moment, and the demand for the system output power P6 rises. Then, when the load power P7 at point B increases to a certain value, the Nth contactor of the main contactor group 18 must be cut off to restore the system output power P6. Therefore, after judging that P1 ≥ set value 1, further continue to judge P1 ≥ P RN+ Set value 1. If it is true, it means that the increment of the load power P7 at load B reaches the compensation power P of the system at this time RN , then the Nth contactor of the main contactor group 18 is cut off. After that, after returning to the step of putting in the N - 1 group of contactors, judge the magnitude of the grid power P1, and execute downward; if it is false, it means that the increment of the load power P7 at load B does not reach the compensation power P of the system at this time RN , there will be reverse power after cutting off the Nth contactor of the main contactor group 18, so after returning to the step of putting in the Nth group of contactors, continue to judge the magnitude of P1 and execute downward. When P1 < set value 1 in this step, it means that after all compensation resistors are put in, the compensation power generated by the compensation circuit breaker 15 is still not enough to make up for the decrease of the load power P7 at B, that is, the photovoltaic power P2 reaches the maximum value P2 MAX , the system output power P6 decreases to the photovoltaic power P2 MAX by 5%, the load power P7 reaches the minimum value, P7 < 5%P2 MAX + Set value 1. At this time, there is no need to continue generating electricity. The anti - reverse current component 9 then trips the second contactor 11 and cuts off all the contactors from the 1st to the Nth of the main contactor group 18. The system is in the off - grid state. After off - grid, the grid power P1 = the load power P7 at B. Judge the magnitude of the grid power P1. When P1 (i.e., the load power P7) is greater than 5% of the photovoltaic power P2 MAX , then start grid connection (close the second contactor 11), that is, P1 > 5%P2 MAX + Set value 1, return to execute closing the second contactor 11 at (V) and execute downward; when P1 ≤ 5%P2 MAX + Set value 1, it means that the load power P7 is still too small. After a delay of 0.5 seconds (adjustable), continue to judge until the condition is met.

[0074] In this way, by circulating, the system output power of the anti - reverse current device can be adjusted by the resistance compensation power, preventing reverse power generation and maximizing the guarantee of photovoltaic power generation running on the grid.

[0075] Note 1: When due to weather reasons or approaching dusk, assuming the load remains unchanged (greater than 5%P2 MAX ), when the photovoltaic output decreases, the system will gradually cut off all the contactors of the main contactor group 18 from the back to the front in turn. After cutting to the 1st group of the main contactor group 18, it is necessary to judge whether the photovoltaic output reaches the minimum value. If it reaches the minimum value, that is, P2 < 5%P2 MAX , then trip the second contactor and cut off all the contactors from the 1st to the Nth of the main contactor group 18, and wait for the next grid connection; when P2 ≥ 5%P2 MAX , continue to enter step (VI) and execute downward.

[0076] Note 2: The resistance values R1, R2, R3... RN of the resistor string 19 can be the same or different, and can be adjusted according to the load fluctuation; the minimum output power P2 of the photovoltaic power P2 MIN does not necessarily have to be greater than 5%P2 MAX , as long as it is greater than the power P of the resistor R1 R1 is sufficient to ensure that the system is in the best working state.

[0077] Note 3: To ensure that the system automatically enters the standby state at night, multiple sets of timing modes can be used to control the operation and standby of the system.

[0078] Note 4: To ensure the adjustment accuracy while accelerating the response time, sub-contactors 1 to n can also be set under each of the first to N groups of contactors. When coarsely adjusting, the first to N groups of main contactors are used to accelerate the response time. When finely adjusting, the sub-contactors 1 to n are used to improve the adjustment accuracy. If the main contactor group N is taken as 20 and the sub-contactor n is taken as 5, the adjustment accuracy can reach 20×5 = 100 levels; the control signals of the n groups of sub-contactors are controlled by serial communication, and it can be achieved by simply adding a communication interface in the anti-counterflow component 9. This will not be elaborated in this article.

[0079] By repeating this cycle, the output power of the anti-counterflow device system can be adjusted by resistor compensation power, preventing reverse power generation while maximizing the guarantee of photovoltaic power generation operating in the grid.

[0080] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, substitutions, and improvements made within the spirit and principles of the present invention to achieve the adjustment of the output power of the photovoltaic system in the form of increasing or decreasing the resistance shall be included within the protection scope of the present invention.

Claims

1. A distributed photovoltaic power generation anti-backflow device, comprising a grid power supply (1) and a main load circuit (2). The grid power supply (1) is connected to the main load circuit (2) through a power circuit breaker (14). One side of the main load circuit (2) is connected to an AC busbar trunking box (4) through a first contactor (3). The AC busbar trunking box (4) is connected to an inverter (5). The other side of the main load circuit (2) is also branched with a load branch circuit (6). A load circuit breaker (7) and a fourth current transformer (8) are sequentially installed on the load branch circuit (6). It is characterized in that: It further includes an anti-counterflow component (9), a first current transformer (10), a second contactor (11), a third current transformer (12), and a compensation branch (13); The first current transformer (10) is installed between the grid power supply (1) and the power circuit breaker (14); The second contactor (11) is installed between the monitoring point A and the first contactor (3); The third current transformer (12) is installed between the first contactor (3) and the AC busbar box (4); The compensation branch (13) is connected between the second contactor (11) and the first contactor (3). An on-off circuit breaker (15), a second current transformer (16), and a resistor cabinet (17) are sequentially connected to the compensation branch (13); The first current acquisition terminal of the anti-counterflow component (9) is connected to the third current transformer (12); The grouped switching signal of the anti-counterflow component (9) is connected to the resistor cabinet (17); The third current acquisition terminal of the anti-counterflow component (9) is connected to the second current transformer (16); The on-off control signal of the anti-counterflow component (9) is connected to the second contactor (11); A fifth current transformer (20) is installed between the monitoring point A and the second contactor (11). The fourth current acquisition terminal of the anti-counterflow component (9) is connected to the fifth current transformer (20); The voltage acquisition input terminal of the anti-counterflow component (9) is connected to point D on the grid power supply (1); The second current acquisition terminal of the anti-counterflow component (9) is connected to the first current transformer (10); The voltage acquisition output terminal of the anti-counterflow component (9) is connected to point C on the load main circuit (2); The on-off control signal of the anti-counterflow component (9) is connected to the first contactor (3).

2. The distributed photovoltaic power generation anti-counterflow device according to claim 1, wherein: The resistor cabinet (17) includes a main contactor group (18) and a plurality of resistor strings (19). The main contactor group (18) is respectively connected to the grouped switching signal of the anti-counterflow component (9) and the second current transformer (16), and the plurality of resistor strings (19) are respectively connected to the respective sub-contacts of the main contactor group (18).

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