A power generation system backflow prevention control system and method

Abstract

The present application discloses a power generation system backflow prevention control system and method, the method comprises the following steps: detecting the total number N of inverters in the power generation system; if N≤preset value N SET , the inverter output power of the power generation system is controlled by data communication to prevent reverse flow; if N> preset value N SET , the inverter output power of the power generation system is controlled to prevent backflow by a non-communication blind adjustment method based on power calculation. The system is used to implement the above method. Beneficial effects of the present application: Compared with the traditional method, in the scenario with a large number of inverters, the power generation system does not need to interact with the inverter for backflow prevention, which can effectively avoid the problem of the system being in a backflow state for a long time or the load taking power from the power grid for a long time due to long communication time, thereby achieving rapid backflow prevention while reducing the user's electricity cost.

Description

Technical Field

[0001] The present application relates to the field of renewable energy power generation, and in particular to a power generation system anti-backflow control system and method. Background Art

[0002] With the development of the photovoltaic industry, the transformer capacity of power grids in some regions has reached saturation with the installed capacity of photovoltaic projects. The power grid company requires that the electricity generated by the photovoltaic systems built later be consumed by local loads, and the excess electricity is not allowed to be reversely transmitted to the superior power grid through the low-voltage distribution transformer. That is, when too many photovoltaic systems send electricity into the power grid at the same time, it will cause a decline in power quality and easily lead to electrical failures; therefore, anti-backflow control requirements are put forward for photovoltaic systems.

[0003] For the power generation system, reverse flow means that in the power supply and distribution system, the distribution transformer supplies power to the load, and the normal current flows from the grid side to the load. However, when the power of the photovoltaic power generation system is greater than the load power, the load cannot fully absorb it, and the remaining electric energy is fed back into the grid. Since the current is opposite to the normal flow direction, it is called reverse flow.

[0004] Most of the existing photovoltaic power generation system backflow prevention solutions use host polling to collect the output power information of each inverter, and adjust the output power of each inverter after calculation based on the grid power, the number of inverters and the output power of each inverter. The main defects are as follows:

[0005] (1) The existing technology collects the inverter output power information through polling. In the scenario where there are a large number of inverters, the output power of each inverter needs to be collected and communicated, which takes a long time and may cause the power grid to be in a reverse current state for a long time, affecting the quality of the power grid.

[0006] (2) When the load power changes to a level greater than the output power of the power generation system, although the power generation system meets the requirements of the prior art for preventing backflow, it will cause the load to draw power from the grid for a long time, thereby increasing the user's electricity usage costs. Summary of the invention

[0007] One of the purposes of the present application is to provide a power generation system backflow prevention control system that can solve at least one of the defects in the above-mentioned background technology.

[0008] Another object of the present application is to provide a method for preventing backflow in a power generation system that can solve at least one of the defects in the above-mentioned background technology.

[0009] In order to achieve at least one of the above purposes, the technical solution adopted by the present application is: a method for preventing backflow in a power generation system, comprising the following steps: detecting the total number N of inverters in the power generation system; if N ≤ a preset value N SET, the inverter output power of the power generation system is controlled by data communication to prevent reverse flow; if N> preset value N SET , the inverter output power of the power generation system is controlled to prevent backflow by blind adjustment based on grid power detection.

[0010] Preferably, the anti-backflow control for the blind adjustment mode includes the following process: setting the backflow power threshold P th1 and the power grid provides power threshold P th2 ; Check the power grid. If there is current flowing to the grid and the absolute value of the grid power is greater than the reverse power threshold P th1 , the power generation system performs at least one round of power reduction anti-reverse flow control on each inverter based on the current grid power; after completing the anti-reverse flow control, the grid is continuously detected. If it is detected that there is current flowing out of the grid and the absolute value of the grid power is greater than the power threshold P provided by the grid, th2 The power generation system performs at least one round of power increase on each inverter based on the current grid power; if the power generation system needs to perform multiple rounds of power increase on the inverter, the power generation system is suitable for finding the inverter working at the maximum power point during the power adjustment process to first reduce the power, and then over-adjust the power of the inverter that has not reached the maximum power point, and then re-adjust the power of the inverter that has been reduced in the power generation system according to the under-power value before and after the power adjustment.

[0011] Preferably, when the power generation system needs to increase power, the determination of the number of inverter power adjustment rounds includes the following specific process: based on the initial value P of the grid power grid (20), calculate the increased power ΔP21=P allocated to each inverter in the power generation system grid (20) / N; after the inverter power is increased, the grid power P grid (21) is tested to obtain the power change of the power grid after power regulation ΔP = P grid (20)-P grid (21); If ΔP<ΔP21, all inverters in the power generation system are operating at the maximum power point, and there is no need to continue to increase the power; if ΔP=P grid (21), at this time, the output power of the power generation system is equal to the load power, and there is no need to continue power regulation; if ΔP21≤ΔP<P grid (21), at this time, the output power of the power generation system is still less than the load power, and the inverter power needs to be further increased.

[0012] Preferably, the multi-round power regulation of the inverter includes the following specific process: based on the calculated ΔP and ΔP21, the number of inverters X that have not reached the maximum power point in the power generation system is estimated; the power of the inverter that has reached the maximum power point is reduced by ΔP22=(X-1)Pgrid (21) / (NX); After the power reduction is completed, the grid power P grid (22) to detect and calculate the number of inverters that reach the maximum power point in the current power generation system Y = [P grid (22)-P grid (21)] / ΔP22; increase the power of the inverters whose number is X and have not reached the maximum power point, and increase the power by ΔP23=P grid (21); After the power is increased, the grid power P grid (23) Test, if P grid The absolute value of (23) is less than or equal to the power threshold P provided by the power grid. th2 , the power control will be exited, otherwise the inverter that has completed the power reduction of the front wheel will increase the power again, and the increased power ΔP24=P grid (23) / Y.

[0013] Preferably, in the multi-round power regulation process of the inverter, the process of defining a power increase ΔP21 is the first round of power control, the process of defining a power decrease ΔP22 is the second round of power control, the process of defining a power increase ΔP23 is the third round of power control, and the process of defining a power increase ΔP24 is the fourth round of power control; a flag is set for the working status of the inverter, and when performing the first round of power control, the flag position of the inverter that reaches the maximum power point is set to 1, and the flag position of the inverter that does not reach the maximum power point is set to 0; when performing the second round of power control, the power of the inverter with the flag position being 1 is reduced, and the inverter with the flag position being 0 remains unchanged; when performing the third round of power control, the power of the inverter with the flag position being 0 is increased, and the inverter with the flag position being 1 remains unchanged; when performing the fourth round of power control, the power of the inverter with the flag position being 1 is increased, and the inverter with the flag position being 0 remains unchanged.

[0014] Preferably, the number X of inverters that have not reached the maximum power point is estimated by the multiple relationship between ΔP and ΔP21; the specific estimation calculation formula is: (K-1)ΔP21≤ΔP<P grid (21); where K is a constant and the value of X is the maximum value of (K-1).

[0015] Preferably, the anti-backflow control for reducing the inverter power includes the following process: based on the initial value P of the grid power grid (10), calculate the reduced power ΔP11=P allocated to each inverter in the power generation system grid (10) / N; after the inverter power is reduced, the grid power P grid (11) and the current direction are detected; if there is no current flowing to the grid, or the grid power Pgrid The absolute value of (11) is less than or equal to the reverse power threshold P th1 , exit the power reduction control; if there is current flowing to the grid and the grid power P grid The absolute value of (11) is greater than the reverse power threshold P th1 , continue to reduce the power of each inverter, reduce the power ΔP12=P grid (11)×a%, where a is a constant ranging from 0 to 100.

[0016] Preferably, the preset value N SET The calculation formula is as follows:

[0017] T1=N SET ×T collect +T broadcast ;

[0018] Among them, T1 represents the time consumed by the power generation system to use data communication for anti-backflow control, T collect Indicates the communication time of each inverter for anti-backflow control, T broadcast Indicates the time when the inverter issues power commands during power regulation.

[0019] A power generation system backflow prevention control system comprises a monitoring module and a control module; the monitoring module is used to detect a power grid to obtain the current direction and power of the power grid; the control module is communicatively connected to the monitoring module, and the control module is also connected to each inverter of the power generation system; the control module is suitable for communicating with the inverter or issuing power instructions according to the backflow prevention control mode of the power generation system.

[0020] Preferably, the control module adopts a centralized architecture to perform power calculation and control on all inverters; alternatively, the control module adopts a distributed architecture to select one of the inverters as the main inverter to perform power calculation and distribution, and perform power control on the remaining inverters based on the calculation results.

[0021] Compared with the prior art, the beneficial effects of this application are:

[0022] (1) Compared with the traditional method, in the scenario with a large number of inverters, the power generation system does not need to interact with the inverter for reverse flow control, which can effectively avoid the problem of the system being in a reverse flow state for a long time or the load taking power from the grid for a long time due to long communication time, thereby achieving rapid reverse flow prevention while reducing the user's electricity cost.

[0023] (2) The calculation process of the power command in the present application is simple, and there is no need for the inverter to autonomously calculate the power command and determine whether to execute the power command, thereby saving computing resources and accelerating the speed of power adjustment without affecting the control function of the system itself. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the working logic for anti-backflow control for this application.

[0025] Figure 2 Schematic diagram of the workflow for anti-backflow power reduction for this application.

[0026] Figure 3 A schematic diagram of a rotation adjustment for a specific example of power reduction for backflow prevention in the present application.

[0027] Figure 4 Schematic diagram of the workflow for increasing power after backflow prevention is completed for this application.

[0028] Figure 5 A rotation diagram of one specific example of power increase after backflow prevention is completed in this application.

[0029] Figure 6 It is a schematic diagram of the structure of the anti-backflow control system of the power generation system in this application. DETAILED DESCRIPTION

[0030] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that in the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0031] In the description of the present application, it should be noted that directional words, such as the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating directions and positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of narrating the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and cannot be understood as limiting the specific scope of protection of the present application.

[0032] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0033] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be connected, detachably connected, or integrated; it can be mechanically connected or electrically connected; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0035] The terms "including" and "having" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0036] One aspect of the present application provides a method for preventing backflow in a power generation system. Figure 1As shown, one preferred embodiment includes the following steps: detecting the total number N of inverters in the power generation system; if N ≤ a preset value N SET , the inverter output power of the power generation system is controlled by data communication to prevent reverse flow; if N> preset value N SET , the inverter output power of the power generation system is controlled to prevent backflow by blind adjustment based on grid power detection.

[0037] It should be known that when a traditional power generation system performs anti-backflow control, it is necessary to obtain the power data of each inverter and calculate the power adjustment command based on the obtained results. As those skilled in the art know, there is a delay time in signal communication, and the delay time is related to the amount of data required for communication. Therefore, when the number of inverters included in the power generation system is small, the traditional data communication method can be used for the anti-backflow control of the power generation system; and when the number of inverters included in the power generation system is large, the non-communication blind adjustment mode based on grid power detection can be used for the anti-backflow control of the power generation system. That is, the power adjustment command of the inverter is mainly obtained through the detection of the grid power and related calculations, and there is no need to communicate and obtain the power parameters of the inverter itself.

[0038] Therefore, compared with traditional anti-backflow control methods, the anti-backflow control method of the power generation system of the present application can realize anti-backflow control of the inverter without the need for power information interaction in scenarios with a large number of inverters. It can effectively avoid the problem of the system being in a reverse current state for a long time or the load drawing power from the power grid for a long time due to long communication time. While achieving rapid backflow prevention, it can also effectively reduce the user's electricity cost.

[0039] It is understandable that the anti-backflow control mode of the power generation system in this embodiment can also be judged from the perspective of time. Specifically, based on the number of inverters N in the current power generation system, combined with the communication time T of each inverter for anti-backflow control, collect , the power command issuing time when the inverter performs power regulation T broadcast ; The time consumption T1 of the current power generation system using data communication for anti-backflow control and the time consumption T2 of non-communication blind adjustment for anti-backflow control can be calculated in advance. By comparing the sizes of T1 and T2, the best anti-backflow control method for the power generation system can be selected; that is, when T1≥T2, the power generation system preferably uses blind adjustment for anti-backflow control; when T1<T2, the power generation system preferably uses data communication for anti-backflow control.

[0040] The specific calculation formula for T1 and T2 is: T1=N SET ×T collect +T broadcast ; T2 = 4 × Tbroadcast When T1 ≥ T2, the communication time T of each inverter for anti-reverse flow control is collect , and the power command issuing time T when the inverter performs power regulation broadcast If the value of T1 is known, the preset value N can be obtained by the calculation formula of T1. SET The specific value of .

[0041] In this embodiment, the main idea of ​​the anti-backflow control of the power generation system based on the working scenario of the power generation system is: when the load power is reduced and the output power of the power generation system is greater than the load power, the power generation system may supply reverse power to the power grid. At this time, the output power of the power generation system needs to be reduced to avoid excess power being fed into the power grid. As the power of the load increases, the output power of the power generation system is less than the load power, so that the load needs to draw power from the power grid, which will increase the user's electricity usage cost. At this time, under the premise of ensuring anti-backflow, the output power of the power generation system needs to be increased to the maximum power or basically close to the load power to meet the power demand of the load. Based on the above ideas, the specific process of anti-backflow control using non-communication blind adjustment is described in detail below.

[0042] Specifically, the anti-backflow control for the blind adjustment method includes the following process: setting the backflow power threshold P th1 and the power grid provides power threshold P th2 . Detect the power grid. If there is current flowing to the grid and the absolute value of the grid power is greater than the reverse power threshold P th1 The power generation system performs at least one round of anti-reverse flow control on each inverter by reducing the power based on the current grid power.

[0043] After the anti-reverse flow control is completed, the grid is continuously tested. If it is detected that there is current flowing out of the grid and the absolute value of the grid power is greater than the power threshold P provided by the grid, th2 , the power generation system performs at least one round of power increase on each inverter based on the current grid power. If the power generation system needs to perform multiple rounds of power increase on the inverter, the power generation system can find the inverter working at the maximum power point during the power adjustment process and first reduce the power, then over-adjust the power of the inverter that has not reached the maximum power point, and then re-adjust the power of the inverter that has been reduced in the power generation system according to the under-power value before and after the power adjustment.

[0044] For ease of understanding, the power reduction and power increase processes during the anti-backflow control process of the power generation system will be described in detail below.

[0045] 1. When there is current flowing to the grid and the absolute value of the grid power is greater than the reverse power threshold P th1 Power reduction to prevent backflow control.

[0046] like Figure 2 As shown, the anti-reverse flow control for reducing the inverter power includes the following process: based on the initial value P of the grid power grid (10), calculate the reduced power ΔP11=P allocated to each inverter in the power generation system grid (10) / N.

[0047] According to the calculated power reduction ΔP11, a power command is issued to each inverter of the power generation system, and each inverter reduces the power after receiving the power command. After the inverter completes the power reduction, the current grid power P grid (11) and the current direction are detected.

[0048] If there is no current flowing to the grid, it means that the output power of the power generation system is less than the load power, and the power reduction control can be exited. Then, it can be checked whether there is current flowing out of the grid and whether the grid power meets the power threshold P provided by the grid. th2 If all the requirements are met, the power generation system can be upgraded under the premise of preventing backflow. The specific process will be described in detail in the subsequent content.

[0049] If the grid power P grid The absolute value of (11) is less than or equal to the reverse power threshold P th1 , indicating that the output power of the power generation system is basically consistent with the load power at this time, and the power reduction control can also be exited.

[0050] If there is current flowing to the grid and the grid power P grid The absolute value of (11) is still greater than the reverse power threshold P th1 , the power of each inverter will continue to be reduced. At this time, the reduced power ΔP12=P grid (11) A power command is issued to each inverter of the power generation system according to the calculated power reduction ΔP12, and each inverter reduces the power after receiving the power command.

[0051] It should be known that, from the above process, the inverter power reduction includes two rounds of power control process, one of which corresponds to reducing the power by ΔP11, and the other corresponds to reducing the power by ΔP12. In the power control process corresponding to reducing the power by ΔP12, since each inverter in the power generation system receives the instruction to reduce the power by ΔP12, as long as one inverter in the power generation system reduces the power by ΔP12, the reverse flow phenomenon can be eliminated.

[0052] It should also be known that in a round of power control corresponding to a power reduction of ΔP12, since each inverter in the power generation system receives an instruction to reduce the power ΔP12, the power of the power generation system may drop significantly, that is, the load needs to draw power from the grid in a short period of time, resulting in an increase in the user's electricity cost.

[0053] In this embodiment, in order to avoid excessive power drop of the power generation system, the power grid power P after the first round of power control can be grid (11) is used to judge if the grid power P grid If the value of (11) is too large, the value of the power reduction ΔP12 in the next round of power control process can be appropriately reduced. Therefore, in this embodiment, the power reduction ΔP12 can be set to ΔP12=P grid (11)×a%, where a is a constant ranging from 0 to 100.

[0054] It should be noted that if the value of a is too small, the output power of the power generation system may still not meet the anti-reverse flow control after the power of each inverter is reduced by ΔP12, and at least one round of power control process needs to be continued, which may increase the duration of the reverse flow phenomenon and the time of system power adjustment. Therefore, in order to reduce the output power of the power generation system by an appropriate amount while increasing the power adjustment speed to meet the requirements of relevant regulations, the value of a needs to be reasonably set according to the actual working conditions.

[0055] For ease of understanding, the power reduction control of the inverter will be described in detail below using a specific example.

[0056] Specifically, Figure 3 As shown, the inverters of the power generation system are numbered as inverter #1, inverter #2, inverter #3, ..., inverter #N-1, inverter #N. Initially, the initial value of the grid power is P grid (10), at this time, the current output power of each inverter in the power generation system is P in the order of numbering. 11 , P 12 , P 13 ,……,P 1N-1 , P 1N ; Among them, the output power P corresponding to inverter #3 13 <ΔP11.

[0057] When the first round of power control corresponding to the power reduction ΔP11 is performed, the power of each inverter is reduced by ΔP11. 13 <ΔP11, during this process, the power reduction of inverter #3 is ΔP11´=P 13That is, after the first round of power control is completed, the output power of inverter #3 is reduced to 0. At this time, the current output power of each inverter in the power generation system is P 11 -ΔP11,P 12 -ΔP11, 0, ..., P 1N-1 -ΔP11,P 1N -ΔP11; among which, except for inverter #3, the output powers of other inverters are greater than ΔP12.

[0058] When the second round of power control corresponding to the power reduction of ΔP12 is performed, the power of each inverter is reduced by ΔP12. Since the output power of inverter #3 is already 0, inverter #3 will not be able to reduce the power during this process. Then after completing the second round of power control, the current output power of each inverter in the power generation system is P in the order of numbering. 11 -ΔP11-ΔP12, P 12 -ΔP11-ΔP12, 0, ..., P 1N-1 -ΔP11-ΔP12, P 1N -ΔP11-ΔP12; can also be expressed as P 11 -ΔP11-P grid (11) P 12 -ΔP11-P grid (11), 0, ..., P 1N-1 -ΔP11-P grid (11) P 1N -ΔP11-P grid (11).

[0059] From the above content, it can be seen that in the second round of power control, only one inverter in the power generation system needs to be able to complete the power reduction P grid (11), and in the above example, after completing the second round of power control, the output power of the power generation system is lower than the load power by (N-2) P grid (11), which is sufficient to meet the requirements of backflow prevention. Correspondingly, the load needs to draw power from the grid, and the power drawn is (N-2) P grid (11); Since the value of N is large, the load power consumption is large, which in turn increases the user's electricity cost. Therefore, the best solution for the anti-backflow control of the power generation system is to ensure that the power generation system is at the maximum output power or the output power is consistent with the load power while meeting the anti-backflow control. Therefore, after completing the above anti-backflow control, it is necessary to continue to increase the power of the power generation system to ensure that the power generation system can operate in a state closest to the load power.

[0060] 2. When there is current flowing out of the grid and the absolute value of the grid power is greater than the power threshold P provided by the gridth2 Power up control.

[0061] In this embodiment, for the scenario where the power increase of the power generation system includes single-round regulation and multi-round regulation, since the control processes of multi-round regulation and single-round regulation are different, the number of inverter power regulation rounds of the power generation system can be determined first; the specific determination process is as follows:

[0062] like Figure 4 As shown, based on the initial value of the grid power P grid (20), calculate the increased power ΔP21=P allocated to each inverter in the power generation system grid (20) / N. A power command is issued to each inverter of the power generation system according to the calculated downward power ΔP21, and each inverter increases the power after receiving the power command.

[0063] After the inverter completes the power increase, the current grid power P grid (21) Perform detection; According to the obtained grid power P grid (21), the power change of the power grid before and after power regulation ΔP=P grid (20)-P grid (21) The power change ΔP of the power grid is judged, and the number of power regulation rounds of the power generation system is judged based on the judgment result.

[0064] If ΔP<ΔP21, it means that all inverters in the power generation system are running at the maximum power point, so the power generation system will not be able to provide more power, that is, the power generation system does not need to continue to increase power and will exit the power increase control. The number of power adjustment rounds of the power generation system in this scenario is a single round, which corresponds to the process of increasing power by ΔP21.

[0065] If ΔP=P grid (21), indicating that all inverters in the power generation system can perform power reduction ΔP21, and at this time the output power of the power generation system is exactly equal to the load power, so the power generation system does not need to continue power regulation and will exit power increase control. The number of power regulation rounds of the power generation system in this scenario is a single round, which corresponds to the process of power increase ΔP21.

[0066] If ΔP21≤ΔP<P grid (21), at this time, the output power of the power generation system is still less than the load power, and the inverter needs to continue to increase the power. That is, the number of power adjustment rounds of the power generation system in this scenario is multiple rounds, among which the first round of power control corresponds to the process of power increase ΔP21.

[0067] In this embodiment, Figure 4As shown, the multi-round power regulation of the inverter includes the following specific processes: Based on the calculated ΔP and ΔP21, the number of inverters that have not reached the maximum power point in the power generation system is estimated. The power of the inverter that has reached the maximum power point is reduced by ΔP22=(X-1)P grid (21) / (NX). After the power reduction is completed, the grid power P grid (22) to detect and calculate the number of inverters that reach the maximum power point in the current power generation system Y = [P grid (22)-P grid (21)] / ΔP22. The power of the inverters that have not reached the maximum power point is increased by ΔP23=P grid (21). After the power increase is completed, the grid power P grid (23) Test, if P grid The absolute value of (23) is less than or equal to the power threshold P provided by the power grid. th2 , the power control will be exited, otherwise the inverter that has completed the power reduction of the front wheel will increase the power again, and the increased power ΔP24=P grid (23) / Y.

[0068] It should be known that in the multi-round power regulation process of the inverter, the process of power increase ΔP21 can be defined as the first round of power control, the process of power decrease ΔP22 can be defined as the second round of power control, the process of power increase ΔP23 can be defined as the third round of power control, and the process of power increase ΔP24 can be defined as the fourth round of power control. The second round of power control is to ensure that the overall output power of the power generation system will not be greater than the load power in the third round of power control to avoid reverse flow. The number of inverters Y that reach the maximum power point obtained during the second round of power control can correct the estimated value X. If the overall maximum output power of the power generation system is greater than or equal to the load power, then after the above four rounds of power control, the output power of the power generation system will be adjusted to the load power; if the overall maximum output power of the power generation system is less than the load power, then after the above four rounds of power control, the power generation system will output at the maximum power.

[0069] It can be understood that for the estimated value X, the estimated calculation can be performed through the multiple relationship between ΔP and ΔP21. Specifically, when ΔP21≤ΔP<2ΔP21, it means that at most one inverter has not reached the maximum power point, and X=1 can be set at this time; when 2ΔP21≤ΔP<3ΔP21, it means that at most two inverters have not reached the maximum power point, and X=2 can be set at this time. The maximum value of ΔP is ΔP<P grid (21), so the calculation formula of the estimated value X can be expressed as (K-1)ΔP21≤ΔP<P grid(21); where K represents a constant and the value of X can be the maximum value of (K-1).

[0070] In this embodiment, when the above-mentioned multi-round power control is performed on the power generation system, in order to ensure accurate control of the inverter, a flag bit can be set for the inverter. That is, a flag bit is set in the main control program of the inverter. When the inverter reaches the maximum power point, the flag bit can be set to 1. After completing the power boost control, the flag bits of all inverters are reset to 0. Therefore, in the multi-round power adjustment process of the power generation system, when the first round of power control is performed, the flag bit of the inverter that has reached the maximum power point can be set to 1, and the flag bit of the inverter that has not reached the maximum power point can be set to 0. When the second round of power control is performed, the power of the inverter whose flag bit is 1 in the first round of power control is reduced, and the inverter whose flag bit is 0 remains unchanged. When the third round of power control is performed, the power of the inverter whose flag bit is 0 in the first round of power control is increased, and the inverter whose flag bit is 1 remains unchanged; when the fourth round of power control is performed, the power of the inverter whose flag bit is 1 in the first round of power control is increased, and the inverter whose flag bit is 0 remains unchanged.

[0071] For ease of understanding, the process of performing multiple rounds of power increase of the power generation system will be described in detail below with reference to specific examples.

[0072] Specifically, Figure 5 As shown, the inverters of the power generation system are numbered as inverter #1, inverter #2, inverter #3, ..., inverter #N-1, inverter #N. Initially, the initial value of the grid power is P grid (20), at this time, the current output power of each inverter in the power generation system is P in the order of numbering. 21 , P 22 , P 23 ,……,P 2N-1 , P 2N ; Among them, the output power P corresponding to inverter #3 23 At the MPPT, ie, maximum power point, the initial flag position of inverter #3 can be set to 1, and the initial flag positions of the other inverters can be set to 0.

[0073] When the first round of power control is performed, the power of all inverters in the power generation system is increased by ΔP21; since inverter #3 is already operating at the maximum power point, the output power of inverter #3 will remain unchanged. Since the difference between the current output power of inverter #1 and inverter #N and their respective maximum power points is greater than ΔP21, the output power of inverter #1 and inverter #N will be increased to P 21 +ΔP21 and P 2N+ΔP21. The difference between the current output power of inverter #2 and inverter #N-1 and their respective maximum power points is less than ΔP21, so the output power of inverter #2 and inverter #N-1 will be increased to P 22 +ΔP21´ and P 2N-1 +ΔP21〞, and at this time the output powers of inverter #2 and inverter #N-1 are both at the maximum power point, so the flag bits of inverter #2 and inverter #N-1 are set to 1, while the flag bits of inverter #1 and inverter #N continue to remain 0.

[0074] Since the power increase of inverter #2 and inverter #N-1 has not reached ΔP21, the output power of the power generation system is still less than the load power after the first round of power control. At this time, a second round of power control is required. In the second round of power control, the power of inverter #2, inverter #3 and inverter #N-1 with a flag bit of 1 can be reduced by ΔP22. At this time, the output power of inverter #2, inverter #3 and inverter #N-1 is P 22 +ΔP21´-ΔP22, P 23 -ΔP22 and P 2N-1 +ΔP21"-ΔP22. After the second round of power control, it can be ensured that all inverters of the power generation system operate below the maximum power point.

[0075] Then the third round of power control is performed, and the power of the inverter whose flag is 0 after the first round of power control is increased by ΔP23. If each inverter in the power generation system can complete the power increase by ΔP23 after the third round of power control, it can be ensured that the output power of the power generation system is exactly equal to the load power. When the difference between the output power of inverter #1 before the third round of power control and the maximum power point is less than ΔP23, the power of inverter #1 only needs to be increased by ΔP23´ to reach the maximum power point, and the output power of inverter #N can meet the increase requirement of ΔP23. Then after the third round of power control, the output power of inverter #1 is P 21 +ΔP21+ΔP23´, and at this time inverter #1 has reached the maximum power point, and the output power of inverter #N is P 2N +ΔP21+ΔP23.

[0076] Since inverter #1 did not meet the power regulation requirements in the third round of power control, the fourth round of power control is required. Since the inverters with the flag bit 0 were overregulated in the third round of power control, the output power of some inverters with the flag bit 0 reached the maximum power point. Although the remaining inverters with the flag bit 0 did not reach the maximum power point, they may have been very close to the maximum power point after multiple rounds of power increase. The inverters with the flag bit 1 were power-reduced in the second round of power control, so that the output power of the inverters with the flag bit 1 has a large upward adjustment space, and when the fourth round of power control is performed, after the increase in the third round of power control, the value of the increased power ΔP24 of the fourth round of power control is obviously smaller than ΔP22, so inverter #2, inverter #3 and inverter #N-1 can all meet the power increase ΔP24 without reaching the maximum power point. At this time, the output powers of inverter #2, inverter #3 and inverter #N-1 are P respectively. 22 +ΔP21´-ΔP22+ΔP24, P 23 -ΔP22+ΔP24 and P 2N-1 +ΔP21〞-ΔP22+ΔP24.

[0077] It is understandable that the overall idea of ​​the above-mentioned multiple rounds of power control is to first find the inverter at the maximum power point, and then reduce its power so that all inverters of the power generation system are below the maximum power point, and then perform at least one round of power increase on the inverters with different flags according to the flags, so that the output power of the power generation system gradually approaches the load power until it is equal to the load power, or the power generation system outputs the maximum power. It should be noted that the flag of the inverter is only adjusted after the first round of power control, and the flag of the inverter will remain unchanged in the subsequent multiple rounds of power control.

[0078] At the same time, the present application simplifies the calculation process for power instructions, that is, regulating power, and does not require the inverter to autonomously calculate the power instructions and determine whether to execute the power instructions, thereby saving computing resources and speeding up power adjustment without affecting the control function of the system itself.

[0079] Another aspect of the present application provides a power generation system anti-backflow control system, such as Figure 6 As shown, one preferred embodiment includes a monitoring module and a control module. The monitoring module is used to detect the power grid to obtain the current direction and power of the power grid; the control module is connected to the monitoring module in communication, and the control module is also connected to each inverter of the power generation system; the control module is suitable for communicating with the inverter or issuing power instructions according to the anti-backflow control mode of the power generation system.

[0080] It should be known that the specific structure and working principle of the monitoring module and the control module are well-known technologies to those skilled in the art, so they will not be elaborated in detail here. The common control module adopts an anti-backflow controller. Taking the three-phase inverter system as an example, the common monitoring module can adopt a three-phase meter; of course, for other forms of inverter systems, other devices that meet the requirements can be used.

[0081] It should also be known that the anti-backflow controller communicates with the three-phase electric meter to monitor the grid information, and the anti-backflow controller communicates with the power generation system to achieve power control of the inverter. The specific communication method can be selected according to the actual needs of technical personnel in this field, for example, 485 communication method can be used.

[0082] It is understandable that when the number of inverters in the power generation system is small, that is, N≤N SET When N>N, the anti-backflow controller can receive the output power status of each inverter in the power generation system to perform anti-backflow communication control; when the number of inverters in the power generation system is large, that is, N>N SET At this time, the anti-backflow controller only needs to receive the grid power monitored by the three-phase meter to calculate the regulated power. Then, the anti-backflow controller only needs to send power instructions to the inverter through communication according to the calculated regulated power, without the need to communicate and receive the power parameters of the inverter.

[0083] In this embodiment, there are many specific arrangements for the control module. For example, the control module can adopt a centralized architecture, that is, the power calculation and control of all inverters. Of course, the control module can also adopt a distributed architecture, that is, one of the inverters is selected as the main inverter for power calculation and distribution, and the power of the remaining inverters is controlled based on the calculation results. The specific arrangements of the centralized architecture and the distributed architecture are well-known technologies for those skilled in the art, so they will not be elaborated in detail here.

[0084] The above describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and the specification only describe the principles of the present application. The present application may have various changes and improvements without departing from the spirit and scope of the present application, and these changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the attached claims and their equivalents.

Claims

1. A method for preventing backflow in a power generation system, characterized in that: The steps include: Detect the total number N of inverters in the power generation system; If N≤preset value N SET , the inverter output power of the power generation system is controlled against reverse flow by using data communication; If N>preset value N SET , the inverter output power of the power generation system is controlled to prevent reverse flow by blind adjustment based on grid power detection; The anti-backflow control for the blind adjustment method includes the following processes: Set the reverse power threshold P th1 and the power grid provides power threshold P th2 ; Detect the power grid. If there is current flowing to the grid and the absolute value of the grid power is greater than the reverse power threshold P th1 , the power generation system performs at least one round of anti-reverse flow control of power reduction on each inverter based on the current grid power; After the anti-reverse flow control is completed, the grid is continuously tested. If it is detected that there is current flowing out of the grid and the absolute value of the grid power is greater than the power threshold P provided by the grid, th2 , the power generation system increases the power of each inverter for at least one round based on the current grid power.

2. The anti-backflow control method for a power generation system according to claim 1, characterized in that: If the power generation system needs to perform multiple rounds of power increases on the inverter, the power generation system is suitable for finding the inverter operating at the maximum power point during the power adjustment process and first reducing the power, and then over-adjusting the power of the inverter that has not reached the maximum power point, and then re-adjusting the power of the inverter that has been power-reduced in the power generation system according to the under-generated power value before and after the power adjustment.

3. The anti-backflow control method for a power generation system according to claim 2, characterized in that: When the power generation system needs to increase power, the determination of the number of inverter power increase rounds includes the following specific processes: Based on the initial value of grid power P grid (20), calculate the increased power ΔP21=P allocated to each inverter grid (20) / N; After the inverter power is increased, the grid power P grid (21) is tested to obtain the power change of the power grid after power regulation ΔP = P grid (20)-P grid (twenty one); If ΔP<ΔP21, all inverters in the power generation system are operating at the maximum power point, and there is no need to continue to increase the power; If ΔP=P grid (21), at this time, the output power of the power generation system is equal to the load power, and no further power regulation is required; If ΔP21≤ΔP<P grid (21), at this time, the output power of the power generation system is still less than the load power, and the inverter power needs to be further increased.

4. The power generation system backflow prevention control method according to claim 3, characterized in that: The multi-round power regulation of the inverter includes the following specific processes: Based on the calculated ΔP and ΔP21, estimate the number X of inverters that have not reached the maximum power point in the power generation system; The inverter that has reached the maximum power point is powered down by ΔP22=(X-1)P grid (21) / (NX); After the power reduction is completed, the grid power P grid (22) to detect and calculate the number of inverters that reach the maximum power point in the current power generation system Y = [P grid (22)-P grid (21)] / ΔP22; The power of the inverters that have not reached the maximum power point is increased by ΔP23=P grid (twenty one); After the power increase is completed, the grid power P grid (23) Test, if P grid The absolute value of (23) is less than or equal to the power threshold P provided by the power grid. th2 , the power control will be exited, otherwise the inverter that has completed the power reduction of the front wheel will increase the power again, and the increased power ΔP24=P grid (23) / Y.

5. The anti-backflow control method for a power generation system according to claim 4, characterized in that: In the multi-round power regulation process of the inverter, the process of power adjustment ΔP21 is defined as the first round of power control, the process of power adjustment ΔP22 is defined as the second round of power control, the process of power adjustment ΔP23 is defined as the third round of power control, and the process of power adjustment ΔP24 is defined as the fourth round of power control; A flag is set for the working status of the inverter. When performing the first round of power control, the flag of the inverter that has reached the maximum power point is set to 1, and the flag of the inverter that has not reached the maximum power point is set to 0; When performing the second round of power control, the power of the inverter whose flag position is 1 is reduced, and the power of the inverter whose flag position is 0 remains unchanged; When the third round of power control is performed, the power of the inverter whose flag position is 0 is increased, and the power of the inverter whose flag position is 1 remains unchanged; When the fourth round of power control is performed, the power of the inverters whose flag position is 1 is increased, and the power of the inverters whose flag position is 0 remains unchanged.

6. The power generation system backflow prevention control method according to claim 4, characterized in that: The number X of inverters that have not reached the maximum power point is estimated through the multiple relationship between ΔP and ΔP21; The specific estimation calculation formula is: (K-1)ΔP21≤ΔP<P grid (21); where K is a constant and the value of X is the maximum value of (K-1).

7. The power generation system backflow prevention control method according to claim 2, characterized in that: The anti-reverse flow control for inverter power reduction includes the following process: Based on the initial value of grid power P grid (10), calculate the reduced power ΔP11=P allocated to each inverter in the power generation system grid (10) / N; After the inverter power is reduced, the grid power P grid (11) and current direction detection; If there is no current flowing to the grid, or the grid power P grid The absolute value of (11) is less than or equal to the reverse power threshold P th1 , exit the power reduction control; If there is current flowing to the grid and the grid power P grid The absolute value of (11) is greater than the reverse power threshold P th1 , continue to reduce the power of each inverter, reduce the power ΔP12=P grid (11)×a%, where a is a constant ranging from 0 to 100.

8. The power generation system backflow prevention control method according to any one of claims 1 to 7, characterized in that: Default value N SET The calculation formula is as follows: T1=N SET ×T collect +T broadcast ; Among them, T1 represents the time consumed by the power generation system to use data communication for anti-backflow control, T collect Indicates the communication time of each inverter for anti-backflow control, T broadcast Indicates the time when the inverter issues power commands during power regulation.

9. A power generation system backflow prevention control system, used to implement the power generation system backflow prevention control method according to any one of claims 1 to 8, characterized in that: Including monitoring module and control module; The monitoring module is used to detect the power grid to obtain the current direction and power of the power grid; The control module is communicatively connected with the monitoring module, and the control module is also connected with each inverter of the power generation system; the control module is suitable for communicating with the inverter or issuing power instructions according to the anti-backflow control mode of the power generation system.

10. The power generation system backflow prevention control system according to claim 9, characterized in that: The control module adopts a centralized architecture to perform power calculation and control on all inverters; Alternatively, the control module adopts a distributed architecture, selects one of the inverters as a main inverter to perform power calculation and distribution, and performs power control on the remaining inverters based on the calculation results.

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