Photovoltaic surplus power utilization method and photovoltaic surplus power utilization system

Abstract

The present invention relates to a photovoltaic surplus power utilization method and a photovoltaic surplus power utilization system, which are applied to a photovoltaic system having at least two inverters. The photovoltaic system operates in a grid-connected mode or a grid-disconnected mode. An output end of each inverter is connected to an alternating-current coupling point. A controller measures the power or voltage at the alternating-current coupling point and determines, on the basis of the power or the voltage, whether there is surplus power at the alternating-current coupling point. When it is detected that there is surplus power, the power at the alternating-current coupling point is distributed to an inverter which has no surplus power. When all the inverters reach a maximum-power operation state, grid-connected delivery processing or grid-disconnected step-down processing is performed on the power at the alternating-current coupling point. The present application can achieve the efficient utilization of photovoltaic surplus power, and also can avoid the impact of communication latency on photovoltaic power supply control, thereby improving the timeliness and accuracy of photovoltaic power control, such that photovoltaic energy can be utilized to the maximum extent.

Description

Photovoltaic surplus power utilization method and photovoltaic surplus power utilization system Technical Field

[0001] The present invention relates to the field of photovoltaic control technology, 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 a central controller to manage it in a unified manner. During the management process, two basic requirements must be met: on the one hand, it should respond to basic needs such as grid scheduling 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 products.

[0003] Currently, the power supply control method for parallel power generation scenarios mostly selects one device as the master and the remaining devices as slaves. The master device comprehensively determines whether the current unit can increase or decrease its output based on the PV control status, energy storage operating status, and meter power feedback reported by the slave devices. It then outputs a current-sharing power instruction to achieve unified scheduling of its own device and the remaining units. However, due to the intermittent, volatile, and unpredictable nature of photovoltaic power generation, as well as the communication delays at each stage of the real-time exchange of key information, it is difficult for the master device to accurately assess the green power output capacity of the current unit, which in turn leads to performance impairment and curtailment during the control process.

[0004] In addition, for the full application of photovoltaic power, the currently commonly used control strategies are all 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 and algorithm levels, 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 each slave as the control target and uniformly dispatches the power. However, it ignores the transfer of surplus electricity from renewable energy between various 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 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 method for utilizing surplus photovoltaic power, which is applied to a photovoltaic system having 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 detected. 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 operating 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 has reached a maximum power operating 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 based on 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 based on 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.

[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 its 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 power 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 maximum grid-connected 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 system islimit When the grid connection threshold value P is less 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 connection 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, if the maximum grid-connected power limit value P configured by the photovoltaic system is limit When the grid connection threshold value P is less 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;

[0018] When the power at the AC coupling point is not less than the grid connection 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 .

[0019] According to one embodiment of the present invention, the state where all inverters reach the maximum power includes two working states:

[0020] First, all inverters are in a state of generating surplus power;

[0021] Second, some inverters are in a state of generating surplus power, while the rest are in a state of absorbing saturated energy.

[0022] According to one embodiment of the present invention, the controller is either independently provided or integrated into a control module of a certain inverter.

[0023] According to one embodiment of the present invention, the controller is independently provided in a gateway or an electrical box.

[0024] 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 at the AC coupling point and determines whether to perform regulation based on the voltage at the AC coupling point. When performing regulation, the power at the AC coupling point is processed to the 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.

[0025] 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 has reached a maximum power operating 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 based on the remaining power status at the AC coupling point.

[0026] According to one embodiment of the present invention, the controller determines, based on power parameters fed back by each inverter, whether each inverter is an inverter that generates surplus power or an inverter that does not generate surplus power, 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;

[0027] 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.

[0028] According to one embodiment of the present invention, when all inverters reach the maximum power operating 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.

[0029] 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 ;

[0030] 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 with no excess power;

[0031] 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 with no redundant power, the voltage at the AC coupling point is stepped down or limited.

[0032] According to one embodiment of the present invention, the state where all inverters reach the maximum power includes two working states:

[0033] First, all inverters are in a state of generating surplus power;

[0034] Second, some inverters are in a state of generating surplus power, while the rest are in a state of absorbing saturated energy.

[0035] According to one embodiment of the present invention, the controller is either independently provided or integrated into a control module of a certain inverter.

[0036] According to one embodiment of the present invention, the controller is independently provided in a gateway or an electrical box.

[0037] 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 terminals of each inverter are 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:

[0038] 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 detection unit;

[0039] The inverter status detection unit determines whether each inverter has surplus power or has reached the maximum power working state based on the power parameters fed back by each inverter;

[0040] 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;

[0041] The grid-connected transmission unit is configured to transmit the power at the AC coupling point to the grid when all inverters reach the maximum power working state.

[0042] 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 terminals of each inverter are 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:

[0043] 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 based on the voltage detected;

[0044] The inverter status detection unit determines whether each inverter has surplus power or has reached the maximum power working state based on the power parameters fed back by each inverter;

[0045] a current sharing processing unit configured to process the power at the AC coupling point to an inverter with no excess power when the voltage at the AC coupling point exceeds a voltage threshold;

[0046] The voltage adjustment unit is configured to step down the voltage at the AC coupling point when all inverters reach the maximum power operating state.

[0047] Compared with the prior art, the advantages and beneficial effects of the photovoltaic surplus power utilization method of the present invention patent application are:

[0048] 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 entire 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 power limit value can be achieved, ensuring that the grid-connected power of the grid after grid connection is adjustable, and ensuring the compliance and controllability of grid-connected power transmission.

[0049] 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 brought about by 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 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 utilization of photovoltaic energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] 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:

[0051] FIG1 is a schematic diagram of a control flow of a method for utilizing surplus photovoltaic power according to an embodiment of the present invention, wherein the photovoltaic system is in a grid-connected mode;

[0052] FIG2 is a schematic diagram of control logic of a grid connection threshold according to an embodiment of the present invention;

[0053] FIG3 is a schematic diagram of a control flow of a method for utilizing surplus photovoltaic power according to another embodiment of the present invention, wherein the photovoltaic system is in an off-grid mode;

[0054] FIG4 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;

[0055] FIG5 is a schematic structural 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

[0056] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0057] 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.

[0058] Example 1:

[0059] This embodiment describes a method for utilizing surplus photovoltaic power, which is applied to a photovoltaic system having at least two inverters. In this embodiment, the photovoltaic system operates in a grid-connected mode. The grid-connected mode here means that the grid and the inverter are connected to the grid, rather than grid-connected power transmission. Whether the excess electricity generated by photovoltaic power is connected to the grid (i.e., grid-connected power transmission) is determined based on the final output of all inverters.

[0060] The output end of each inverter is connected to an 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 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 using the surplus power utilization method provided in the embodiment of the present application.

[0061] First, let's explain the concept of surplus power. This refers to the excess power a device has after meeting local load demands and charging the energy storage battery. For example, the surplus power at the inverter refers to the excess photovoltaic power remaining after meeting the local load demands of the inverter and charging the energy storage battery connected to the inverter.

[0062] It is understandable 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.

[0063] As for the detection of the photovoltaic surplus power of each inverter, it is performed separately in each inverter. Each inverter counts its own power and sends the 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 power surplus status at the AC coupling point. In other words, the estimation of photovoltaic surplus power is "localized" in each inverter, so that the inverter reports its own photovoltaic power generation status in a timely manner, rather than the traditional photovoltaic surplus power estimation in the controller. This not only avoids the adverse effects caused by the intermittent, fluctuating and unpredictable nature of photovoltaic power generation, but also has real-time reporting, which can avoid the adverse effects caused by communication delays and estimated calculation lags in the real-time interaction process of key information. This enables the controller of the present application to accurately evaluate the current green power output capacity of each inverter, improve the real-time and accuracy of photovoltaic power control, and thus maximize the utilization of photovoltaic energy.

[0064] 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 brought about by 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 utilization of photovoltaic energy.

[0065] In the process of adjusting the power of the inverter itself according to the output instruction of the controller, as shown in the process of FIG1 :

[0066] If there is surplus power at the AC coupling point, the controller determines whether each inverter is generating surplus power or not based on the power parameters fed back by each inverter. The inverter generating surplus power is designated as the first inverter, and the inverter not generating surplus power is designated as the second inverter. The power at the AC coupling point is then transferred to the second inverter. The definition of "first inverter" and "second inverter" herein is determined based on the operating conditions of each inverter and changes dynamically. For example, as the operating state of the inverter changes, the photovoltaic power generation power of an inverter that originally did not generate surplus power may increase, but may become an inverter that generates surplus power, in other words, change from a "second inverter" to a "first inverter." Similarly, as the operating state of the inverter changes, the photovoltaic power generation power of an inverter that originally generated surplus power may decrease, but may become an inverter that does not generate surplus power, in other words, change from a "first inverter" to a "second inverter." This method uses the real-time operating state of each inverter as the basis for controlling surplus power utilization.

[0067] As shown in FIG1 , the photovoltaic system operates in grid-connected mode. When the power at the AC coupling point is transferred 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.

[0068] When the PV system is in grid-connected mode, the power at the AC coupling point will increase as the system's photovoltaic power generation increases only when all inverters have reached maximum power. Otherwise, as long as even one inverter has not reached maximum power, the controller can transfer excess photovoltaic power to the corresponding inverter for energy absorption, effectively controlling the power at the AC coupling point to zero. When all inverters have reached maximum power, representing their maximum absorption capacity, any remaining excess power will prevent the AC coupling point from being controlled to zero. Therefore, strict regulation of grid-connected power is necessary in grid-connected mode.

[0069] The aforementioned "all inverters reach the maximum power working state" includes two working states:

[0070] First, all inverters are in a state of generating surplus power;

[0071] Second, some inverters are in a state of generating surplus power, while the rest are in a state of absorbing saturated energy.

[0072] In the grid-connected mode, in order to ensure the compliance and controllability of grid-connected power transmission, the controller sets the grid-connected threshold P 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 and transmits power, 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 fixed values ​​can ensure that the grid-connected power transmitted from the grid coupling point to the grid is stable within the normal range, making the grid-connected power transmission compliant and controllable.

[0073] In one embodiment, the grid connection threshold P BREF The AC coupling point is connected to the grid and transmits power, and the grid-connected power can be maintained within the maximum grid-connected power limit range.

[0074] 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. This will undoubtedly lead to a contradiction. That is, after detecting that the power at the AC coupling point is greater than zero (there is surplus photovoltaic power), power sharing control should be performed and the surplus photovoltaic power should be transferred to the second inverter. However, this also meets the grid connection conditions, which will limit the transfer of surplus photovoltaic power between the second inverters. Based on this, the conditions for the situation where the maximum grid power limit is small are optimized, as shown in Figure 2:

[0075] If the maximum grid-connected power limit value P of the photovoltaic system configuration is limit When the grid connection threshold value P is less than k% of the total capacity of all inverters in the photovoltaic system (k is a coefficient between 1 and 100, or k is a coefficient between 0 and 100), the grid connection threshold value P is set to 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 power surplus at the AC coupling point but the power is less than the grid connection threshold P BREF When , it is possible to ensure that the second inverter can absorb the power at the AC coupling point;

[0076] When the power at the AC coupling point is not less than the grid connection threshold P BREF When the grid connection condition is triggered, the maximum power limit value P limit It is obviously 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 connection 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 sends 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 .

[0077] In addition, if the maximum grid power limit value P limit If it is zero, after the aforementioned grid-connection threshold and power detection threshold are lowered, the power at the AC coupling point is greater than the grid-connection threshold and power detection threshold, so the second inverter can still absorb power from the AC coupling point. At the same time, PI adjustment can be performed on the power at the AC coupling point to reduce the power at the AC coupling point.

[0078] The above controller can be independently set up and can be independently set up in a gateway or an electrical box. Each inverter is communicated with the controller. 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 power surplus status at the AC coupling point.

[0079] 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, thus forming a master-slave control.

[0080] 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, and at the same time realize 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.

[0081] Each inverter evaluates its own generated power and transmits measured results of excess PV power. The controller detects power at the AC coupling point and provides power feedback control. This simplifies overall control and enables energy transfer between inverters, maximizing the utilization of renewable energy. Furthermore, in grid-connected mode, zero-power connection or even connection at the maximum grid power limit can be achieved, ensuring grid compliance and controllable grid power after connection.

[0082] Example 2:

[0083] This embodiment describes a method for utilizing surplus photovoltaic power, which is applied to a photovoltaic system having at least two inverters, operating in an off-grid mode. The workflow of the method for utilizing surplus photovoltaic power in the off-grid mode is shown in FIG3 . The output terminals of each inverter are connected to an AC coupling point. A controller detects the voltage at the AC coupling point and determines whether to perform regulation based on the voltage at the AC coupling point. When performing regulation, the power processing at the AC coupling point is distributed to the inverter without surplus power. During this process, the port voltage of the first inverter is circulated to the second inverter, achieving power distribution between the first and second inverters. If all inverters reach the maximum power operating state, the voltage at the AC coupling point is reduced or limited.

[0084] 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 ;

[0085] 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 with no excess power;

[0086] 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 with no redundant power, the voltage at the AC coupling point is stepped down or limited.

[0087] Each inverter calculates its own power and sends power parameters to the controller. The controller determines whether each inverter has surplus power or has reached its maximum power operating state based on the power parameters fed back by each inverter. The controller adjusts and controls the operation of the AC coupling point and each inverter based on the surplus power status at the AC coupling point. The controller determines whether each inverter is generating surplus power or not generating surplus power based on the power parameters fed back by each inverter. The inverter generating surplus power is designated as the first inverter, and the inverter not generating surplus power is designated as the second inverter.

[0088] When the voltage at the AC coupling point is detected to be greater than the set voltage threshold V AREF When the AC coupling point is changed, the output voltages of the first and second inverters are adjusted to accommodate voltage changes at the AC coupling point. The first inverter raises its output voltage and transmits it to the AC coupling point, thereby raising the voltage at the AC coupling point. The second inverter lowers its own voltage, thereby lowering the voltage at the AC coupling point and reducing the voltage at the AC coupling point that was raised by the first inverter. In this way, power transfer from the first inverter to the second inverter is achieved through voltage circulation between the inverters.

[0089] 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 excess 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 PV system and generally refers to the overvoltage and undervoltage range of the PV system.

[0090] The state where all inverters reach maximum power includes two working states:

[0091] First, all inverters are in a state of generating surplus power;

[0092] Second, some inverters are in a state of generating surplus power, while the rest are in a state of absorbing saturated energy.

[0093] The above controller can be independently set up and can be independently set up in a gateway or an electrical box. Each inverter is communicated with the controller. 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 power surplus status at the AC coupling point.

[0094] 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, thus forming a master-slave control.

[0095] 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, and at the same time realize 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.

[0096] 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 results. In the entire 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 power limit value can be achieved to ensure the compliance of the grid operation after grid connection and the controllability of the grid power.

[0097] Regardless of whether the PV system is in grid-connected or off-grid mode, the surplus power of each inverter in the PV system can be divided into three conditions: no surplus power in all inverters, surplus power in all inverters, and surplus power in some inverters. In summary, the energy flow between inverters and the power control at the AC coupling point can be controlled based on these six operating conditions: no surplus power in grid-connected mode, surplus power in all inverters in grid-connected mode, surplus power in some inverters in grid-connected mode, no surplus power in off-grid mode, surplus power in all inverters in off-grid mode, and surplus power in some inverters in off-grid mode.

[0098] The above six working conditions are specifically described. The control flow of the photovoltaic surplus power utilization method in the grid-connected mode is shown in Figure 2, and the control flow of the photovoltaic surplus power utilization method in the off-grid mode is shown in Figure 3:

[0099] 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 causes the other second inverters without surplus power to 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 not greater than P. BREF Fixed value.

[0100] 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 to avoid affecting the normal operation of other conventional control links.

[0101] 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 not greater than P BREF Fixed value.

[0102] When the photovoltaic system is in off-grid 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, the output voltage of the first inverter is temporarily adjusted to increase the voltage of the first inverter and raise the voltage of the AC coupling point. 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 the other second inverters without surplus power to make corresponding adjustments and reduce their own output voltages, so that the surplus photovoltaic power can be "transferred" from the port of the first inverter to the second inverter in the form of circulating current, maximizing the utilization of photovoltaic power. 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 through the second inverter alone. 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 ).

[0103] 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 to avoid affecting the normal operation of other conventional control links.

[0104] In the off-grid mode of the photovoltaic system, when all inverters generate surplus power, that is, all inverters are first inverters, each inverter feeds its own 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.

[0105] Example 3:

[0106] This embodiment describes a photovoltaic surplus power utilization system, which is applied to a photovoltaic system having at least two inverters. The photovoltaic system operates in a grid-connected mode, and the output terminals of each inverter are connected to an AC coupling point. As shown in FIG4 , the photovoltaic surplus power utilization system includes a power detection unit, an inverter status detection unit, a power distribution unit, and a grid-connected transmission unit. The following are examples of the photovoltaic surplus power utilization system:

[0107] 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 detection unit;

[0108] The inverter status detection unit determines whether each inverter has surplus power or has reached the maximum power working state based on the power parameters fed back by each inverter;

[0109] 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;

[0110] The grid-connected transmission unit is configured to transmit the power at the AC coupling point to the grid when all inverters reach the maximum power working state.

[0111] Example 4:

[0112] This embodiment describes a photovoltaic surplus power utilization system, which is applied to a photovoltaic system having at least two inverters. The photovoltaic system operates in an off-grid mode, and the output terminals of each inverter are connected to an AC coupling point. As shown in FIG5 , the photovoltaic surplus power utilization system includes a voltage detection unit, an inverter status detection unit, a current sharing unit, and a voltage adjustment unit, wherein:

[0113] 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 based on the voltage detected;

[0114] The inverter status detection unit determines whether each inverter has surplus power or has reached the maximum power working state based on the power parameters fed back by each inverter;

[0115] a current sharing processing unit configured to process the power at the AC coupling point to an inverter with no excess power when the voltage at the AC coupling point exceeds a voltage threshold;

[0116] 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.

[0117] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A photovoltaic surplus power utilization method, applied to a photovoltaic system having at least two inverters, characterized in that: When the photovoltaic system operates in grid-connected mode, the output of each inverter is connected to the AC coupling point. The controller detects the power at the AC coupling point and determines whether there is surplus power at the AC coupling point based on the power. If surplus power is detected, the power at the AC coupling point is distributed to the inverter with no surplus power. If all inverters reach the maximum power operating state, the power at the AC coupling point is connected to the grid and sent out.

2. The photovoltaic surplus power utilization method according to claim 1, 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 has reached a maximum power operating 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 based on the power surplus status at the AC coupling point.

3. The photovoltaic surplus power utilization method according to claim 1, 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 based on the power parameters fed back by each inverter, and records the inverter that generates surplus power as the first inverter and the inverter that does not generate surplus power as the 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.

4. The photovoltaic surplus power utilization method according to claim 3, 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 its absorbed power.

5. The photovoltaic surplus power utilization method according to any one of claims 1 to 4, 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 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 power of the AC coupling point.

6. The photovoltaic surplus power utilization method according to claim 5, characterized in that: The grid connection threshold P BREF The grid-connected power transmission power of the AC coupling point is equal to the maximum grid-connected power limit value configured for the photovoltaic system.

7. The photovoltaic surplus power utilization method according to claim 5, characterized in that: If the maximum grid-connected power limit value P of the photovoltaic system configuration is limit When the grid connection threshold value P is less 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; When the power at the AC coupling point is not less than the grid connection 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 .

8. The photovoltaic surplus power utilization method according to claim 5, characterized in that: If the maximum grid-connected power limit value P of the photovoltaic system configuration is limit When the grid connection threshold value P is less 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 connection 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 .

9. The photovoltaic surplus power utilization method according to claim 1, characterized in that: The state where all inverters reach 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.

10. The photovoltaic surplus power utilization method according to claim 1, characterized in that: The controller is either independently provided or integrated into a control module of a certain inverter.

11. The photovoltaic surplus power utilization method according to claim 10, characterized in that: The controller is independently arranged in a gateway or an electrical box.

12. A photovoltaic surplus power utilization method, applied to a photovoltaic system having at least two inverters, characterized in that: When the photovoltaic system operates in off-grid mode, the output of each inverter is connected to the AC coupling point. The controller detects the voltage at the AC coupling point and determines whether to perform regulation based on the voltage at the AC coupling point. When performing regulation, the power at the AC coupling point is processed to the inverter with no residual power. If all inverters reach the maximum power operating state, the voltage at the AC coupling point is reduced or limited.

13. The photovoltaic surplus power utilization method according to claim 12, 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 has reached a maximum power operating 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 based on the power surplus status at the AC coupling point.

14. The photovoltaic surplus power utilization method according to claim 12, characterized in that: The controller determines, based on power parameters fed back by each inverter, whether each inverter is an inverter that generates surplus power or an inverter that does not generate surplus power, 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 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.

15. The photovoltaic surplus power utilization method according to any one of claims 12 to 14, characterized in that: 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.

16. The photovoltaic surplus power utilization method according to claim 15, 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 voltage circulation between each inverter is processed, the power processing at the AC coupling point is distributed to the inverter with no excess power; 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 with no redundant power, the voltage at the AC coupling point is stepped down or limited.

17. The photovoltaic surplus power utilization method according to claim 15, characterized in that: The state where all inverters reach 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.

18. The photovoltaic surplus power utilization method according to claim 12, characterized in that: The controller is either independently provided or integrated into a control module of a certain inverter.

19. The photovoltaic surplus power utilization method according to claim 18, characterized in that: The controller is independently arranged in a gateway or an electrical box.

20. A photovoltaic surplus power utilization system, applied to a photovoltaic system having at least two inverters, characterized in that: The photovoltaic system operates in grid-connected mode, with the output of each inverter connected to the AC coupling point. The photovoltaic surplus power utilization system includes a power detection unit, an inverter status 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 detection unit; The inverter status detection unit determines whether each inverter has surplus power or has reached the maximum power working state based on 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 reach the maximum power working state.

21. A photovoltaic surplus power utilization system, applied to a photovoltaic system having at least two inverters, characterized in that: When the photovoltaic system operates in off-grid mode, the output of each inverter is connected to the AC coupling point. The photovoltaic surplus power utilization system includes a voltage detection unit, an inverter status detection unit, a current sharing unit, and a voltage adjustment unit. 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 based on the voltage detected; The inverter status detection unit determines whether each inverter has surplus power or has reached the maximum power working state based on the power parameters fed back by each inverter; a current sharing processing unit configured to process the power at the AC coupling point to an inverter with no excess 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 operating state.

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