Photovoltaic residual electricity utilization method and photovoltaic residual electricity utilization system

Abstract

The invention relates to a photovoltaic residual electricity utilization method and a photovoltaic residual electricity utilization system, which are applied to a photovoltaic system with at least two inverters, the photovoltaic system works in a grid-connected or off-grid mode, and the output end of each inverter is connected to an alternating current coupling point. The controller detects the power or voltage of the alternating current coupling point, judges whether the alternating current coupling point has residual power or not according to the power or voltage, and distributes the power at the alternating current coupling point to the inverters without residual power when detecting that the residual power exists; and if all the inverters reach the maximum power working state, grid-connected output or off-grid voltage reduction processing is carried out on the power at the AC coupling point. According to the invention, efficient utilization of photovoltaic residual electricity can be realized, the influence of communication delay on photovoltaic power supply control can be avoided, the real-time performance and accuracy of photovoltaic power control are improved, and photovoltaic energy can be utilized to the maximum extent.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic control, and in particular to a photovoltaic surplus power utilization method and a photovoltaic surplus power utilization system. Background Art

[0002] For the scenario of multi-machine parallel collaborative power supply of renewable energy power generation equipment, it is necessary to abstract the central controller for unified management. In the management process, two basic requirements must be met: on the one hand, it should respond to basic needs such as grid dispatching needs and local load power supply needs; on the other hand, it should maximize the utilization of renewable energy and improve the economy and environmental friendliness of the product.

[0003] At present, the power supply control method for parallel-connected scenarios is mostly to select one device as the host and the other devices as slaves. The host comprehensively judges whether the current unit can increase or reduce output based on the photovoltaic control status, energy storage operation status, meter power feedback, etc. reported by the slave, and outputs the current-sharing power instruction to achieve unified scheduling of its own equipment and other units. However, due to the intermittent, volatile, and unpredictable nature of photovoltaic power generation, as well as the communication delays in each link of the real-time interaction of key information, it is difficult for the host to accurately evaluate the green power output capacity of the current unit, which leads to performance impairment and abandoned light during the control process.

[0004] In addition, for the full application of photovoltaic power, the commonly used control strategies are currently based on the knowledge of the maximum photovoltaic power for regulation. However, the maximum photovoltaic power can only be known more accurately when the MPPT control reaches the maximum power point. Therefore, it is difficult to obtain the accurate maximum photovoltaic power from both the physical level and the algorithm level, which leads to non-negligible errors in the control strategies that use this as the key parameter. On the other hand, the parallel control strategy for off-grid mode usually takes the voltage and phase consistency between the slaves as the control target and uniformly dispatches the power. However, it ignores the transfer of surplus electricity from renewable energy between the devices, making it difficult to achieve efficient utilization of photovoltaics. Summary of the invention

[0005] A main purpose of the present invention is to overcome at least one of the above-mentioned defects, and to provide a photovoltaic surplus power utilization method and a photovoltaic surplus power utilization system, which can realize the efficient utilization of photovoltaic surplus power, and at the same time avoid the influence of communication delay on photovoltaic power supply control, improve the real-time and accuracy of photovoltaic power control, and maximize the utilization of photovoltaic energy.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a photovoltaic surplus power utilization method, which is applied to a photovoltaic system with at least two inverters, wherein the photovoltaic system operates in a grid-connected mode, the output end of each inverter is connected to an AC coupling point, a controller detects the power of the AC coupling point and determines whether there is surplus power at the AC coupling point based on the power, and when it is detected that there is surplus power, the power at the AC coupling point is distributed to the inverter without surplus power, and when all inverters reach the maximum power working state, the power at the AC coupling point is connected to the grid and sent out.

[0008] According to one embodiment of the present invention, each inverter counts its own power and sends power parameters to the controller. The controller determines whether each inverter has surplus power or reaches the maximum power working state based on the power parameters fed back by each inverter, and adjusts and controls the operation of the AC coupling point and each inverter in combination with the remaining power status at the AC coupling point.

[0009] According to one embodiment of the present invention, the controller determines whether each inverter is an inverter that generates surplus power or an inverter that does not generate surplus power according to power parameters fed back by each inverter, and the inverter that generates surplus power is recorded as a first inverter, and the inverter that does not generate surplus power is recorded as a second inverter.

[0010] When it is detected that there is surplus power at the AC coupling point, the power at the AC coupling point is distributed to the second inverter.

[0011] According to one embodiment of the present invention, in the step of distributing the power at the AC coupling point to the second inverter,

[0012] The power sent from the AC coupling point to the second inverter is adjusted, and the second inverter increases the absorbed power.

[0013] According to one embodiment of the present invention, when all inverters reach the maximum power working state, the controller compares the power of the AC coupling point with the grid connection threshold P BREF In comparison, the power at the AC coupling point is not less than the grid connection threshold P BREF When the AC coupling point is connected to the grid, the controller controls the AC coupling point to be connected to the grid, and the controller regulates the grid-connected power transmission of the AC coupling point.

[0014] According to one embodiment of the present invention, the grid connection threshold P BREF The grid-connected power transmission power of the AC coupling point is equal to the grid-connected maximum power limit value configured for the photovoltaic system.

[0015] According to one embodiment of the present invention, if the maximum grid-connected power limit value P configured by the photovoltaic systemlimit When the grid connection threshold P is smaller than k% of the total capacity of all inverters in the photovoltaic system, the method is initialized. BREF The power monitoring threshold P is set to k% of the total capacity of all inverters to determine whether there is power surplus at the AC coupling point. AREF is set to zero, where k is a coefficient ranging from 1 to 100;

[0016] When the power at the AC coupling point is not less than the grid-connected threshold P BREF When the grid connection threshold is lowered to P' BREF , adjusted P' BREF =P limit , and the power monitoring threshold is synchronously moved down to P' AREF , adjusted P' AREF =P limit -P BREF .

[0017] According to one embodiment of the present invention, the state where all inverters reach the maximum power working state includes two working states:

[0018] First, all inverters are in a state of generating surplus power;

[0019] Second, some inverters are in a state of generating surplus power, while the rest are in a state of absorbing saturated energy.

[0020] According to one embodiment of the present invention, the controller is either independently provided or integrated in a control module of a certain inverter.

[0021] According to one embodiment of the present invention, the controller is independently arranged in a gateway or an electrical box.

[0022] In particular, the present invention also provides a method for utilizing surplus photovoltaic power, which is applied to a photovoltaic system having at least two inverters. The photovoltaic system operates in an off-grid mode, and the output ends of each inverter are connected to an AC coupling point. A controller detects the voltage of the AC coupling point and determines whether to perform regulation based on the voltage of the AC coupling point. When performing regulation, the power at the AC coupling point is processed to an inverter with no surplus power. If all inverters reach the maximum power operating state, the voltage at the AC coupling point is reduced or limited.

[0023] According to one embodiment of the present invention, each inverter counts its own power and sends power parameters to the controller. The controller determines whether each inverter has surplus power or reaches the maximum power working state based on the power parameters fed back by each inverter, and adjusts and controls the operation of the AC coupling point and each inverter in combination with the remaining power status at the AC coupling point.

[0024] According to one embodiment of the present invention, the controller determines whether each inverter is an inverter that generates surplus power or an inverter that does not generate surplus power according to power parameters fed back by each inverter, and the inverter that generates surplus power is recorded as a first inverter, and the inverter that does not generate surplus power is recorded as a second inverter;

[0025] When it is detected that the voltage at the AC coupling point is greater than a set voltage threshold, the output voltages of the first inverter and the second inverter are adjusted to adapt to the voltage change at the AC coupling point.

[0026] According to one embodiment of the present invention, when all inverters reach the maximum power working state, the voltage at the AC coupling point is reduced or limited so that the voltage at the AC coupling point is within an allowable range.

[0027] According to one embodiment of the present invention, the method is configured with a first voltage threshold V AREF and the second voltage threshold V BREF , the first voltage threshold V AREF Less than the second voltage threshold V BREF ;

[0028] When the voltage at the AC coupling point is not less than the first voltage threshold V AREF When the voltage circulation between each inverter is processed, the power processing at the AC coupling point is distributed to the inverter without surplus power;

[0029] When the voltage at the AC coupling point is not less than the second voltage threshold V BREF When the power processing at the AC coupling point is distributed to the inverter without surplus power, the voltage at the AC coupling point is reduced or limited.

[0030] According to one embodiment of the present invention, the state where all inverters reach the maximum power working state includes two working states:

[0031] First, all inverters are in a state of generating surplus power;

[0032] Second, some inverters are in a state of generating surplus power, while the rest are in a state of absorbing saturated energy.

[0033] According to one embodiment of the present invention, the controller is either independently provided or integrated in a control module of a certain inverter.

[0034] According to one embodiment of the present invention, the controller is independently arranged in a gateway or an electrical box.

[0035] In particular, the present invention provides a photovoltaic surplus power utilization system, which is applied to a photovoltaic system having at least two inverters, wherein the photovoltaic system operates in a grid-connected mode, and the output end of each inverter is connected to an AC coupling point. The photovoltaic surplus power utilization system includes a power detection unit, an inverter state detection unit, a power distribution unit and a grid-connected transmission unit, wherein:

[0036] A power detection unit, configured to detect the power of the AC coupling point and determine whether there is surplus power at the AC coupling point based on the power detected by the AC coupling point;

[0037] The inverter state detection unit determines whether each inverter has surplus power or has reached the maximum power working state according to the power parameters fed back by each inverter;

[0038] a power distribution unit configured to distribute the power at the AC coupling point to the inverter without surplus power when surplus power is detected;

[0039] The grid-connected transmission unit is configured to transmit the power at the AC coupling point to the grid when all inverters have reached the maximum power working state.

[0040] In particular, the present invention provides a photovoltaic surplus power utilization system, which is applied to a photovoltaic system having at least two inverters, wherein the photovoltaic system operates in an off-grid mode, and the output end of each inverter is connected to an AC coupling point. The photovoltaic surplus power utilization system includes a voltage detection unit, an inverter state detection unit, a current sharing processing unit and a voltage adjustment unit, wherein:

[0041] a voltage detection unit, configured to detect the voltage at the AC coupling point and determine whether the voltage at the AC coupling point exceeds a set voltage threshold value based on the voltage detection unit;

[0042] The inverter state detection unit determines whether each inverter has surplus power or has reached the maximum power working state according to the power parameters fed back by each inverter;

[0043] a current balancing processing unit configured to process the power at the AC coupling point to an inverter with no surplus power when the voltage at the AC coupling point exceeds a voltage threshold;

[0044] The voltage adjustment unit is configured to step down the voltage at the AC coupling point when all inverters reach the maximum power working state.

[0045] Compared with the prior art, the advantages and beneficial effects of the photovoltaic surplus power utilization method of the patent application of the present invention are:

[0046] The photovoltaic surplus power utilization method and photovoltaic surplus power utilization system of the present application realize the detection of photovoltaic surplus power by evaluating the amount of electricity generated by each inverter, and the controller detects the power or voltage at the AC coupling point, and then performs power regulation or voltage regulation based on the detection result. In the whole surplus power utilization control process, the controller only needs to monitor and control the AC coupling point, and the inverter regulation only needs to be adjusted according to the controller's instructions, making the overall control simpler, and realizing the energy transfer of photovoltaic surplus power between each inverter, maximizing the utilization of renewable energy. In addition, in the grid-connected mode, zero-power grid connection or grid connection with the maximum grid-connected power limit value can be realized, ensuring that the grid-connected power of the power grid after grid connection is adjustable, and ensuring the compliance and controllability of grid-connected power transmission.

[0047] Furthermore, a control module is set in each inverter to realize the "localization" of photovoltaic surplus power detection, so as to realize timely reporting of its own photovoltaic power generation status. Different from the traditional photovoltaic surplus power estimation in the controller, it can avoid the adverse effects of the intermittent, volatile and unpredictable nature of photovoltaic power generation. At the same time, the reporting is real-time, which can avoid the adverse effects of communication delays in the real-time interaction process of key information, so that the controller of the present application can accurately evaluate the green power output capacity of each inverter at present, improve the real-time and accuracy of photovoltaic power control, and thus maximize the utilization of photovoltaic energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0049] Figure 1 is a schematic diagram of a control flow of a photovoltaic surplus power utilization method according to an embodiment of the present invention, wherein the photovoltaic system is in a grid-connected mode;

[0050] Figure 2 is a control logic diagram of a grid connection threshold according to an embodiment of the present invention;

[0051] Figure 3 is a schematic diagram of a control flow of a photovoltaic surplus power utilization method according to another embodiment of the present invention, wherein the photovoltaic system is in an off-grid mode;

[0052] Figure 4 is a schematic structural diagram of a photovoltaic surplus power utilization system according to an embodiment of the present invention, wherein the photovoltaic system is in a grid-connected mode;

[0053] Figure 5It is a structural schematic diagram of a photovoltaic surplus power utilization system according to another embodiment of the present invention, wherein the photovoltaic system is in an off-grid mode. DETAILED DESCRIPTION

[0054] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0056] Embodiment 1:

[0057] This embodiment describes a method for utilizing surplus photovoltaic power, which is applied to a photovoltaic system with at least two inverters. In this embodiment, the photovoltaic system operates in a grid-connected mode. The grid-connected mode here means that the power grid and the inverter are connected to the grid, rather than grid-connected power transmission. Whether the excess electricity generated by photovoltaics is sent to the grid (i.e., grid-connected power transmission) is still determined based on the final output of all inverters.

[0058] The output end of each inverter is connected to an AC coupling point, and the controller detects the power of the AC coupling point and determines whether there is surplus power at the AC coupling point based on the power. When surplus power is detected, the power at the AC coupling point is distributed to an inverter without surplus power or connected to the grid for transmission through the surplus power utilization method provided in the embodiment of the present application.

[0059] First, let's explain a concept: the concept of surplus power. Surplus power refers to the power surplus that still exists after the equipment meets the local load demand and the charging demand of the energy storage battery. For example, the surplus power at the inverter is the photovoltaic power surplus that still exists after the inverter, which is a photovoltaic storage device, meets the local load demand of the inverter and the charging demand of the energy storage battery connected to the inverter.

[0060] It can be understood that in the present application, by detecting the AC coupling point, it is possible to detect whether there is surplus power in the photovoltaic system. If there is surplus power, it indicates that there is an inverter with surplus power output.

[0061] As for the detection of the photovoltaic surplus power of each inverter, it is carried out in each inverter separately. Each inverter counts its own power and sends the power parameters to the controller. The controller determines the working state of each inverter according to the power parameters fed back by each inverter, and adjusts and controls the work of the AC coupling point and each inverter in combination with the power surplus status at the AC coupling point. In other words, the "localization" of the estimation of photovoltaic surplus power in each inverter is realized, and what is realized is that the inverter reports its own photovoltaic power generation status in time, rather than the traditional photovoltaic surplus power estimation in the controller. It can not only avoid the adverse effects caused by the intermittent, volatile and unpredictable nature of photovoltaic power generation, but also the reporting is real-time, which can avoid the adverse effects caused by the communication delay of key information in the real-time interaction process and the estimated calculation lag, so that the controller of the present application can accurately evaluate the green power output capacity of each inverter at present, improve the real-time and accuracy of photovoltaic power control, and thus maximize the use of photovoltaic energy.

[0062] A control module is provided in each inverter, and the control module is configured to adjust the power of the inverter itself according to the output instruction of the controller. A control module is provided in each inverter to realize the "localization" of the detection of photovoltaic surplus power, and to realize the timely reporting of its own photovoltaic power generation status. Different from the traditional photovoltaic surplus power estimation in the controller, it can avoid the adverse effects of the intermittent, volatile and unpredictable nature of photovoltaic power generation. At the same time, the reporting is real-time, which can avoid the adverse effects of communication delays of key information in the real-time interaction process, so that the controller of this application can accurately evaluate the green power output capacity of each inverter at present, improve the real-time and accuracy of photovoltaic power control, and thus maximize the use of photovoltaic energy.

[0063] In the process of adjusting the inverter's own power according to the output instruction of the controller, Figure 1 The process is shown as follows:

[0064] If there is surplus power at the AC coupling point, the controller determines whether each inverter is an inverter that generates surplus power or an inverter that does not generate surplus power according to the power parameters fed back by each inverter, and the inverter that generates surplus power is recorded as the first inverter, and the inverter that does not generate surplus power is recorded as the second inverter, and the power at the AC coupling point is transferred to the second inverter. The definition of "first inverter" and "second inverter" here is determined according to the working conditions of each inverter and is dynamically changed. For example, as the working state of the inverter continues to change, the photovoltaic power generation power of the inverter that originally does not generate surplus power increases and may also change to an inverter that generates surplus power, that is, from the "second inverter" to the "first inverter". Similarly, as the working state of the inverter changes, the photovoltaic power generation power of the inverter that originally generates surplus power decreases and may also change to an inverter that does not generate surplus power, that is, from the "first inverter" to the "second inverter". When performing surplus power utilization control, this method is based on the real-time working state of each inverter.

[0065] like Figure 1 As shown, the photovoltaic system operates in the grid-connected mode, and the power at the AC coupling point is transferred to the second inverter by adjusting the power sent from the AC coupling point to the second inverter, and the second inverter increases the absorbed power.

[0066] When the photovoltaic system is in the grid-connected mode, the power at the AC coupling point will increase with the increase of photovoltaic power generation of the photovoltaic system only when all inverters have reached the maximum power working state. Otherwise, as long as one inverter has not reached the maximum power working state, the controller can transfer the photovoltaic surplus power to the corresponding inverter for energy absorption, that is, the power at the AC coupling point can be controlled to zero. When all inverters have reached the maximum power working state, it means that each inverter has reached the maximum absorption capacity. At this time, if there is still surplus power, it will make it impossible to control the power at the AC coupling point to zero. In the grid-connected mode, it is necessary to consider strict regulation of the grid-connected power.

[0067] The above-mentioned "all inverters reach the maximum power working state" includes two working states:

[0068] First, all inverters are in a state of generating surplus power;

[0069] Second, some inverters are in a state of generating surplus power, while the rest are in a state of absorbing saturated energy.

[0070] In the grid-connected mode, in order to ensure the compliance and controllability of grid-connected power transmission, the grid-connected threshold P is set in the controller. BREF , through the grid-connected threshold P BREFThe setting ensures that the grid-connected power sent from the AC coupling point to the grid is controllable, thereby avoiding the adverse effects of grid-connected power fluctuations on the grid. The controller compares the power of the AC coupling point with the grid-connected threshold P BREF In comparison, the power at the AC coupling point is not less than the grid connection threshold P BREF When the AC coupling point is connected to the grid for power transmission, the second inverter still maintains absorbing power, and the grid-connected power of the grid-connected power transmission is maintained at a grid-connected threshold value P BREF The following set values ​​can ensure that the grid-connected power transmission from the grid coupling point to the power grid is stable within the normal range, making the grid-connected power transmission compliant and controllable.

[0071] In one embodiment, the grid connection threshold P BREF The AC coupling point is connected to the grid for power transmission and the grid power can be maintained within the maximum grid power limit range.

[0072] However, due to restrictions on grid connection in some countries or regions, grid connection must adopt a specific TOU mode, that is, the permission mechanism for grid connection is different in different time periods. For example, grid connection is not allowed during some electricity consumption valleys. In other words, the maximum grid power limit is limited to zero or a very small value, which will undoubtedly lead to a contradiction. That is, after detecting that the power at the AC coupling point is greater than zero (there is photovoltaic surplus power), power equalization should be controlled and the photovoltaic surplus power should be transferred to the second inverter. However, this also meets the grid connection conditions, which will limit the transfer of photovoltaic surplus power between the second inverters. Based on this, the conditions are optimized for the situation where the maximum grid power limit is small, such as Figure 2 As shown:

[0073] If the maximum grid-connected power limit value P of the photovoltaic system configuration limit When the grid connection threshold value P is less than k% (k is a coefficient between 0 and 100) of the total capacity of all inverters in the photovoltaic system, the method is initialized. BREF The power monitoring threshold P is set to k% of the total capacity of all inverters to determine whether there is power surplus at the AC coupling point. AREF Set to zero, so that when there is surplus power at the AC coupling point but the power is less than the grid-connected threshold P BREF When , it is possible to maintain and ensure that the second inverter can absorb the power at the AC coupling point;

[0074] When the power at the AC coupling point is not less than the grid-connected threshold P BREF When the grid connection condition is triggered, the maximum grid power limit value P limit is significantly smaller than the grid connection threshold P at this time BREF, so the power at the AC coupling point is not less than the grid-connected threshold P BREF When the grid connection threshold is lowered to P' BREF , adjusted P' BREF =P limit , and the power monitoring threshold is synchronously moved down to P' AREF , adjusted P' AREF =P limit -P BREF After the grid-connected threshold and the power detection threshold are lowered, if the power at the AC coupling point is greater than the grid-connected threshold and the power detection threshold, the first inverter transmits the power at the AC coupling point to the grid, and the second inverter absorbs power from the AC coupling point, and the grid-connected power is collaboratively controlled to be no greater than the P' BREF The value of .

[0075] In addition, if the maximum grid-connected power limit value P limit If it is zero, after the aforementioned grid-connected threshold and power detection threshold are lowered, the power at the AC coupling point is greater than the grid-connected threshold and the power detection threshold, so the second inverter can still absorb power from the AC coupling point, and at the same time, the power at the AC coupling point can be PI-regulated to reduce the power at the AC coupling point.

[0076] The above controllers can be independently set up, and the controller can be independently set up in a gateway or an electrical box. Each inverter is connected to the controller for communication. Each inverter counts its own power and sends power parameters to the controller. The controller determines the working status of each inverter based on the power parameters fed back by each inverter, and adjusts and controls the operation of the AC coupling point and each inverter in combination with the remaining power status at the AC coupling point.

[0077] The above controller can also directly use the control module of a certain inverter as the host, integrate the main control function into the control module of a certain inverter, communicate with each other, and use the remaining inverters except the host as slaves, thereby forming a master-slave control.

[0078] Both of the above control modes should be protected by this application. The focus of this application is to realize the transfer and absorption of photovoltaic surplus power in each inverter, so that each local inverter can maximize the utilization of photovoltaic power, while realizing reliable power transmission in the grid-connected mode to ensure the stability of the power grid operation, and should not be limited by the specific method adopted by the main control function.

[0079] Each inverter evaluates the amount of electricity it generates and sends out the measured results of the photovoltaic surplus power. The controller detects the power at the AC coupling point and performs power feedback control. The overall control is simpler and can achieve energy transfer of photovoltaic surplus power between each inverter to maximize the use of renewable energy. In addition, in the grid-connected mode, zero-power grid connection or even grid connection with the maximum grid power limit value can be achieved to ensure the compliance of the grid operation after grid connection and the controllability of grid power.

[0080] Embodiment 2:

[0081] This embodiment describes a photovoltaic surplus power utilization method, which is applied to a photovoltaic system having at least two inverters. The photovoltaic system operates in an off-grid mode. The working process of the photovoltaic surplus power utilization method in the off-grid mode is as follows: Figure 3 As shown, the output end of each inverter is connected to an AC coupling point, and the controller detects the voltage of the AC coupling point and determines whether to perform regulation according to the voltage of the AC coupling point. When performing regulation, the power processing at the AC coupling point is distributed to the inverter without surplus power. In this processing process, the port voltage of the first inverter is circulated to the second inverter to realize the processing and distribution of power between the first inverter and the second inverter. If all inverters reach the maximum power working state, the voltage at the AC coupling point is reduced or limited.

[0082] The method of this embodiment is configured with a first voltage threshold V AREF and the second voltage threshold V BREF , the first voltage threshold V AREF Less than the second voltage threshold V BREF ;

[0083] When the voltage at the AC coupling point is not less than the first voltage threshold V AREF When the voltage circulation between each inverter is processed, the power processing at the AC coupling point is distributed to the inverter without surplus power;

[0084] When the voltage at the AC coupling point is not less than the second voltage threshold V BREF When the power processing at the AC coupling point is distributed to the inverter without surplus power, the voltage at the AC coupling point is reduced or limited.

[0085] Each inverter counts its own power and sends power parameters to the controller. The controller determines whether each inverter has surplus power or has reached the maximum power working state according to the power parameters fed back by each inverter, and adjusts and controls the operation of the AC coupling point and each inverter in combination with the power surplus status at the AC coupling point. The controller determines whether each inverter is an inverter that generates surplus power or an inverter that does not generate surplus power according to the power parameters fed back by each inverter, and records the inverter that generates surplus power as the first inverter, and records the inverter that does not generate surplus power as the second inverter;

[0086] When the voltage at the AC coupling point is detected to be greater than the set voltage threshold V AREF When the voltage at the AC coupling point changes, the output voltages of the first inverter and the second inverter are adjusted to adapt to the voltage change at the AC coupling point. The first inverter raises its own output voltage and sends it to the AC coupling point, thereby raising the voltage at the AC coupling point, while the second inverter lowers its own voltage to lower the voltage at the AC coupling point, pulling back the voltage at the AC coupling point raised by the first inverter, thus realizing power transfer from the first inverter to the second inverter by means of voltage circulation between the inverters.

[0087] When all inverters reach the maximum power working state, the voltage at the AC coupling point begins to be greater than the first voltage threshold V AREF And gradually approach the second voltage threshold V BREF , when the voltage at the AC coupling point is not less than the second voltage threshold V BREF When the power processing at the AC coupling point is distributed to the inverter without surplus power, the voltage at the AC coupling point is regulated. The regulation method can adopt existing technologies such as PI regulation to make the voltage at the AC coupling point within the allowable range, that is, to control the voltage at the second voltage threshold V BREF This allowable range can be determined according to the configuration of the photovoltaic system, and generally refers to the voltage range of overvoltage and undervoltage of the photovoltaic system.

[0088] The working state where all inverters reach the maximum power includes two working states:

[0089] First, all inverters are in a state of generating surplus power;

[0090] Second, some inverters are in a state of generating surplus power, while the rest are in a state of absorbing saturated energy.

[0091] The above controllers can be independently set up, and the controller can be independently set up in a gateway or an electrical box. Each inverter is connected to the controller for communication. Each inverter counts its own power and sends power parameters to the controller. The controller determines the working status of each inverter based on the power parameters fed back by each inverter, and adjusts and controls the operation of the AC coupling point and each inverter in combination with the remaining power status at the AC coupling point.

[0092] The above controller can also directly use the control module of a certain inverter as the host, integrate the main control function into the control module of a certain inverter, communicate with each other, and use the remaining inverters except the host as slaves, thereby forming a master-slave control.

[0093] Both of the above control modes should be protected by this application. The focus of this application is to realize the transfer and absorption of photovoltaic surplus power in each inverter, so that each local inverter can maximize the utilization of photovoltaic power, while achieving reliable operation in off-grid mode, ensuring the efficient operation of the photovoltaic system, and should not be limited by the specific method adopted by the main control function.

[0094] In summary, the photovoltaic surplus power utilization method of the present application realizes the detection of photovoltaic surplus power by evaluating the amount of electricity generated by each inverter, and the controller detects the power or voltage at the AC coupling point, and then performs power regulation or voltage regulation based on the detection result. In the whole process of surplus power utilization control, the controller only needs to monitor and control the AC coupling point, and the inverter regulation only needs to be adjusted according to the controller's instructions, making the overall control simpler, and realizing the energy transfer of photovoltaic surplus power between each inverter, maximizing the utilization of renewable energy. In addition, in the grid-connected mode, zero-power grid connection or grid connection with the maximum grid-connected power limit value can be realized to ensure the compliance of the grid operation after grid connection and the controllability of the grid-connected power.

[0095] Regardless of whether the photovoltaic system is in grid-connected mode or off-grid mode, the residual power of each inverter in the photovoltaic system can be divided into three conditions: all inverters do not generate residual power, all inverters generate residual power, and some inverters generate residual power. In summary, it can be divided into six working conditions: all inverters do not generate residual power in grid-connected mode, all inverters generate residual power in grid-connected mode, some inverters generate residual power in grid-connected mode, all inverters do not generate residual power in off-grid mode, all inverters generate residual power in off-grid mode, and some inverters generate residual power in off-grid mode. The energy flow control between inverters and the power control of the AC coupling point are carried out under the above six working conditions.

[0096] The above six working conditions are described in detail. The control process of the photovoltaic surplus power utilization method in the grid-connected mode is as follows: Figure 2As shown in the figure, the control process of the photovoltaic surplus power utilization method in off-grid mode is as follows Figure 3 As shown:

[0097] When the photovoltaic system is in grid-connected mode, when some inverters generate surplus power, that is, there are some first inverters and some second inverters in the photovoltaic system, when the output power of the first inverter with surplus power increases with the maximum power point tracking of the photovoltaic power, at the same time, when the controller detects that the power at the AC coupling point is greater than zero, the controller makes the other second inverters without surplus power reduce power output or increase absorption power, and lowers the power control of the AC coupling point, thereby dynamically realizing the transfer of photovoltaic surplus power between the second inverters and reducing the problem of abandoned light. When there is still surplus power after the surplus power is transferred between the second inverters, that is, each second inverter has reached its maximum absorption capacity, at this time, the power of the AC coupling point is continuously increased. When it is increased to the grid-connected threshold P BREF When the controller sends out a command to control the photovoltaic system to be connected to the grid, the residual power of the photovoltaic system is controlled to the maximum grid power limit value configured by the system or other grid threshold value P not greater than the grid power limit value. BREF Fixed value.

[0098] When the photovoltaic system is in grid-connected mode, when all inverters do not generate surplus power, that is, all inverters are second inverters, the controller controls the use of photovoltaic surplus power without affecting the normal operation of other conventional control links.

[0099] In the grid-connected mode, when all inverters generate surplus power, that is, all inverters are first inverters, each inverter feeds its surplus power to the AC coupling point. When the power of the AC coupling point reaches the grid-connected threshold P BREF The controller controls the photovoltaic system to be connected to the grid, and controls the residual power of the photovoltaic system to the maximum grid power limit value configured by the system or other grid threshold value P not greater than the grid power limit value. BREF Fixed value.

[0100] When the photovoltaic system is in off-grid mode, when some inverters generate surplus power, that is, there are a part of the first inverter and a part of the second inverter in the photovoltaic system, when the output power of the first inverter with surplus power increases with the maximum power point tracking of the photovoltaic power, the output voltage of the first inverter is temporarily adjusted, so that the voltage of the first inverter is increased, and the voltage of the AC coupling point is raised. At the same time, when the controller detects that the voltage of the AC coupling point is greater than the preset voltage threshold, it controls the voltage of other second inverters without surplus power to make corresponding adjustments and reduce their own output voltages, so that the photovoltaic surplus power can be "transferred" from the port of the first inverter to the second inverter in the form of circulating current, maximizing the use of photovoltaics. When there is still surplus power after the transfer between the second inverters, that is, each second inverter has reached its maximum absorption capacity, at this time, the controller cannot control the voltage of the AC coupling point to the first voltage threshold V only through the second inverter. AREF Therefore, the controller performs PI regulation control on the voltage of the AC coupling point to ensure that the voltage of the AC coupling point is controlled within the allowable range (not greater than the second voltage threshold V BREF ).

[0101] When the photovoltaic system is in off-grid mode, when all inverters do not generate surplus power, that is, all inverters are second inverters, the controller controls the use of photovoltaic surplus power without affecting the normal operation of other conventional control links.

[0102] When the photovoltaic system is in off-grid mode, when all inverters generate surplus power, that is, all inverters are first inverters, each inverter feeds its surplus power to the AC coupling point, and the controller performs PI regulation control on the voltage of the AC coupling point to ensure that the voltage of the AC coupling point is controlled within the allowable range.

[0103] The range of k is corrected to a coefficient of 0 to 100. When k is a coefficient between 0 and 1, the control method of the present invention is also applicable. The specific embodiments are as follows:

[0104] Take k = 0.5 as an example. If the maximum grid-connected power limit value P configured for the photovoltaic system limit When the grid connection threshold P is less than 0.5% of the total capacity of all inverters in the photovoltaic system, the method is initialized. BREFSet to 0.5% of the total capacity of all inverters. At this time, the main controller uses 0.5% of the total inverter capacity as the grid-connected point power threshold, which means that during the dynamic transfer of photovoltaic surplus power, the main controller monitors whether the steady state of the grid-connected point is not less than 0.5% of the total inverter capacity. If not, it means that there is no photovoltaic surplus power, or the photovoltaic surplus power has been transferred but there is an inverter that has not reached the maximum power working state. At this time, 0.5% of the total inverter capacity continues to be used as the grid-connected point power threshold; if yes, it means that all inverters have reached the maximum power working state at this time, and then the grid-connected threshold is lowered to P' BREF , adjusted P' BREF =P limit , and the power monitoring threshold is synchronously moved down to P' AREF , adjusted P' AREF =P limit -P BREF ;

[0105] It is worth noting that the value of k does not affect the core idea of ​​the present invention regarding the utilization of surplus power. The difference is only reflected in the threshold value for determining whether all inverters have reached the maximum power working state, which in turn affects the dynamic adjustment time of the threshold.

[0106] Embodiment 3:

[0107] This embodiment describes a photovoltaic surplus power utilization system, which is applied to a photovoltaic system with at least two inverters, wherein the photovoltaic system operates in a grid-connected mode, and the output end of each inverter is connected to an AC coupling point, such as Figure 4 As shown, the photovoltaic surplus power utilization system includes a power detection unit, an inverter state detection unit, a power distribution unit and a grid-connected transmission unit, wherein:

[0108] A power detection unit, configured to detect the power of the AC coupling point and determine whether there is surplus power at the AC coupling point based on the power detected by the AC coupling point;

[0109] The inverter state detection unit determines whether each inverter has surplus power or has reached the maximum power working state according to the power parameters fed back by each inverter;

[0110] a power distribution unit configured to distribute the power at the AC coupling point to the inverter without surplus power when surplus power is detected;

[0111] The grid-connected transmission unit is configured to transmit the power at the AC coupling point to the grid when all inverters have reached the maximum power working state.

[0112] Embodiment 4:

[0113] This embodiment describes a photovoltaic surplus power utilization system, which is applied to a photovoltaic system with at least two inverters, wherein the photovoltaic system operates in an off-grid mode, and the output end of each inverter is connected to an AC coupling point, such as Figure 5 As shown, the photovoltaic surplus power utilization system includes a voltage detection unit, an inverter state detection unit, a current equalization processing unit and a voltage adjustment unit, wherein:

[0114] a voltage detection unit, configured to detect the voltage at the AC coupling point and determine whether the voltage at the AC coupling point exceeds a set voltage threshold value based on the voltage detection unit;

[0115] The inverter state detection unit determines whether each inverter has surplus power or has reached the maximum power working state according to the power parameters fed back by each inverter;

[0116] a current balancing processing unit configured to process the power at the AC coupling point to an inverter with no surplus power when the voltage at the AC coupling point exceeds a voltage threshold;

[0117] The voltage adjustment unit is configured to reduce or limit the voltage at the AC coupling point when all inverters reach the maximum power working state.

[0118] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A photovoltaic surplus power utilization method, applied to a photovoltaic system having at least two inverters, It is characterized in that The photovoltaic system works in off-grid mode, and the output end of each inverter is connected to the AC coupling point. The controller detects the voltage of the AC coupling point and determines whether to adjust according to the voltage of the AC coupling point. When adjusting, the power at the AC coupling point is processed to the inverter with no surplus power. If all inverters reach the maximum power working state, the voltage at the AC coupling point is reduced or limited so that the voltage at the AC coupling point is within the allowable range.

2. The photovoltaic surplus power utilization method according to claim 1, It is characterized in that Each inverter counts its own power and sends power parameters to the controller. The controller determines whether each inverter has surplus power or reaches the maximum power working state according to the power parameters fed back by each inverter, and adjusts and controls the operation of the AC coupling point and each inverter in combination with the power surplus status at the AC coupling point.

3. The photovoltaic surplus power utilization method according to claim 1, It is characterized in that The controller determines whether each inverter is an inverter that generates surplus power or an inverter that does not generate surplus power according to power parameters fed back by each inverter, and records the inverter that generates surplus power as a first inverter, and records the inverter that does not generate surplus power as a second inverter; When it is detected that the voltage at the AC coupling point is greater than a set voltage threshold, the output voltages of the first inverter and the second inverter are adjusted to adapt to the voltage change at the AC coupling point.

4. The photovoltaic surplus power utilization method according to claim 1, It is characterized in that The method is configured with a first voltage threshold V AREF and the second voltage threshold V BREF , the first voltage threshold V AREF Less than the second voltage threshold V BREF ; When the voltage at the AC coupling point is not less than the first voltage threshold V BREF When the power is distributed to the inverter without surplus power, the voltage circulation between each inverter is processed; When the voltage at the AC coupling point is not less than the second voltage threshold V AREF When the power processing at the AC coupling point is distributed to the inverter without surplus power, the voltage at the AC coupling point is reduced or limited.

5. The photovoltaic surplus power utilization method according to claim 1, It is characterized in that The working state where all inverters reach the maximum power includes two working states: First, all inverters are in a state of generating surplus power; Second, some inverters are in a state of generating surplus power, while the rest are in a state of absorbing saturated energy.

6. A photovoltaic surplus power utilization method, applied to a photovoltaic system having at least two inverters, It is characterized in that The photovoltaic system works in the grid-connected mode, and the output end of each inverter is connected to the AC coupling point. The controller detects the power of the AC coupling point and determines whether there is surplus power at the AC coupling point based on it. When surplus power is detected, the power at the AC coupling point is distributed to the inverter without surplus power. If all inverters reach the maximum power working state, the power at the AC coupling point is connected to the grid and sent out.

7. The photovoltaic surplus power utilization method according to claim 6, It is characterized in that Each inverter counts its own power and sends power parameters to the controller. The controller determines whether each inverter has surplus power or reaches the maximum power working state according to the power parameters fed back by each inverter, and adjusts and controls the operation of the AC coupling point and each inverter in combination with the power surplus status at the AC coupling point.

8. The photovoltaic surplus power utilization method according to claim 6, It is characterized in that The controller determines whether each inverter is an inverter that generates surplus power or an inverter that does not generate surplus power according to power parameters fed back by each inverter, and records the inverter that generates surplus power as a first inverter and the inverter that does not generate surplus power as a second inverter. When it is detected that there is surplus power at the AC coupling point, the power at the AC coupling point is distributed to the second inverter.

9. The photovoltaic surplus power utilization method according to claim 8, It is characterized in that In the step of distributing the power at the AC coupling point to the second inverter, The power sent from the AC coupling point to the second inverter is adjusted, and the second inverter increases the absorbed power.

10. The photovoltaic surplus power utilization method according to any one of claims 6 to 9, It is characterized in that When all inverters reach the maximum power working state, the controller compares the power of the AC coupling point with the grid-connected threshold P BREF In comparison, the power at the AC coupling point is not less than the grid connection threshold P BREF When the AC coupling point is connected to the grid, the controller controls the AC coupling point to be connected to the grid, and the controller regulates the grid-connected power transmission of the AC coupling point.

11. The photovoltaic surplus power utilization method according to claim 10, It is characterized in that The grid connection threshold P BREF The grid-connected power transmission power at the AC coupling point is equal to the grid-connected maximum power limit value configured for the photovoltaic system.

12. The photovoltaic surplus power utilization method according to claim 10, It is characterized in that If the maximum grid-connected power limit value P of the photovoltaic system configuration limit When the grid connection threshold P is smaller than k% of the total capacity of all inverters in the photovoltaic system, the method is initialized. BREF The power monitoring threshold P is set to k% of the total capacity of all inverters to determine whether there is power surplus at the AC coupling point. AREF is set to zero, where k is a coefficient ranging from 0 to 100; When the power at the AC coupling point is not less than the grid-connected threshold P BREF When the grid connection threshold is lowered to P' BREF , adjusted P' BREF =P limit , and the power monitoring threshold is synchronously moved down to P' AREF , adjusted P' AREF =P limit -P BREF .

13. The photovoltaic surplus power utilization method according to claim 6, It is characterized in that The working state where all inverters reach the maximum power includes two working states: First, all inverters are in a state of generating surplus power; Second, some inverters are in a state of generating surplus power, while the rest are in a state of absorbing saturated energy.

14. A photovoltaic surplus power utilization system, applied to a photovoltaic system having at least two inverters, It is characterized in that Photovoltaic system works on Off-grid mode Under this condition, the output end of each inverter is connected to the AC coupling point, and the photovoltaic surplus power utilization system includes a voltage detection unit, an inverter state detection unit, a current equalization processing unit and a voltage adjustment unit, wherein: a voltage detection unit, configured to detect the voltage at the AC coupling point and determine whether the voltage at the AC coupling point exceeds a set voltage threshold value based on the voltage detection unit; The inverter state detection unit determines whether each inverter has surplus power or has reached the maximum power working state according to the power parameters fed back by each inverter; a current balancing processing unit configured to process the power at the AC coupling point to an inverter with no surplus power when the voltage at the AC coupling point exceeds a voltage threshold; The voltage adjustment unit is configured to step down the voltage at the AC coupling point when all inverters reach the maximum power working state.

15. A photovoltaic surplus power utilization system, applied to a photovoltaic system having at least two inverters, It is characterized in that The photovoltaic system works in the grid-connected mode, and the output end of each inverter is connected to the AC coupling point. The photovoltaic surplus power utilization system includes a power detection unit, an inverter state detection unit, a power distribution unit and a grid-connected transmission unit, among which: A power detection unit, configured to detect the power of the AC coupling point and determine whether there is surplus power at the AC coupling point based on the power detected by the AC coupling point; The inverter state detection unit determines whether each inverter has surplus power or has reached the maximum power working state according to the power parameters fed back by each inverter; a power distribution unit configured to distribute the power at the AC coupling point to the inverter without surplus power when surplus power is detected; The grid-connected transmission unit is configured to transmit the power at the AC coupling point to the grid when all inverters have reached the maximum power working state.

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