CN111697626A

CN111697626A - Photovoltaic power station, power generation control method and string inverter

Info

Publication number: CN111697626A
Application number: CN202010633187.4A
Authority: CN
Inventors: 陈鹏; 徐清清; 楚洪法; 刘雷; 陈佶阳
Original assignee: Sungrow Power Supply Co Ltd
Current assignee: Sungrow Power Supply Co Ltd
Priority date: 2020-07-02
Filing date: 2020-07-02
Publication date: 2020-09-22

Abstract

The invention provides a photovoltaic power station, a power generation control method and a string inverter, which are applied to the technical field of photovoltaic power generation, wherein a direct current shunt box in the power station comprises a parallel input end and a plurality of shunt output ends, each direct current shunt box is connected with at least one direct current combiner box, each string inverter is connected with at least one direct current shunt box, and each MPPT circuit in the string inverter is connected with at least one shunt output end in the direct current shunt box, based on the scheme, the MPPT power shared by 1 way of MPPT circuit or 2 ways of MPPT circuits in the centralized inverter in the prior art can be dispersed into more MPPT circuits to ensure that each string inverter can normally work, only the centralized inverter needs to be cancelled in the process of transforming the old photovoltaic power station, the direct current shunt box and the string inverter are added on the original basis, and the connection relation among all the parts is established according to the content, the transformation of the photovoltaic power station can be completed, and the transformation workload is small.

Description

Photovoltaic power station, power generation control method and string inverter

Technical Field

The invention relates to the technical field of photovoltaic power generation, in particular to a photovoltaic power station, a power generation control method and a string inverter.

Background

Fig. 1 is a power station layout commonly used in a photovoltaic power station in the prior art, as shown in the figure, a plurality of photovoltaic strings in the power station are connected in series and parallel to an input end of a dc combiner box, the dc combiner box combines the dc of each connected photovoltaic string and outputs the dc to a centralized inverter, the centralized inverter performs MPPT control, the ac obtained after inversion is output to a transformer, and finally, the transformer performs corresponding conversion on the ac voltage and then transmits the ac voltage to an ac power grid, so as to meet the power demand of a load.

In the practical application of the power station layout, the centralized inverter mainly performs the MPPT function and the inversion function, and therefore, the centralized inverter can not only invert the direct current into the alternating current, but also perform MPPT control based on the converged direct current side.

However, in the early construction of the photovoltaic power station, the centralized inverter technology is still in a starting stage, and most of devices used in the inverter are low in efficiency, so that the overall working efficiency of the centralized inverter is low, and even the overall power generation of the photovoltaic power station is affected. Therefore, how to modify a photovoltaic power station using an old centralized inverter to improve the power generation amount of the photovoltaic power station becomes a technical problem to be solved urgently by technical personnel in the field.

Disclosure of Invention

The invention provides a photovoltaic power station, a power generation control method and a string inverter, and aims to solve the problem that the overall power generation amount of the photovoltaic power station is low due to the use of an old centralized inverter in the prior art.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

in a first aspect, the present invention provides a photovoltaic power plant comprising at least one dc combiner box, at least one dc splitter box, and at least one string inverter including a multi-way MPPT circuit, wherein,

the input side of each direct current combiner box is connected with at least one photovoltaic group string;

the direct current shunt box comprises a parallel input end and a plurality of shunt output ends, and the direct current shunt box is used for shunting and outputting direct current input by the parallel input end through each shunt output end;

the parallel input end of each direct current shunt box is connected with the output side of at least one direct current confluence box;

each group of serial inverters is connected with at least one direct current shunt box, and any MPPT circuit is connected with at least one shunt output end;

each string inverter performs MPPT control based on its own MPPT circuit, and outputs ac power to an ac power grid.

Optionally, the dc combiner boxes connected to the dc splitter boxes are different from each other.

Optionally, the shunt output ends connected to the MPPT circuits in the same path belong to the same dc shunt box, and the shunt output ends connected to the MPPT circuits are different from each other.

Optionally, the dc shunting box includes: a box body and a shunt circuit arranged in the box body, wherein,

the shunt circuit comprises a parallel input circuit and a multi-path shunt output circuit;

one end of the parallel input circuit is used as a parallel input end of the direct current shunt box, and the other end of the parallel input circuit is connected with one end of each shunt output circuit respectively;

and the other end of each shunt output line is used as the output end of the direct current shunt box.

Optionally, the parallel input line is provided with a dc switch.

Optionally, the shunt output line includes a positive line and a negative line, wherein,

at least one of the positive electrode circuit and the negative electrode circuit is provided with an overcurrent protection module.

Optionally, the overcurrent protection module includes a dc fuse.

Optionally, the dc shunting box includes a forced air-cooled dc shunting box or a natural air-cooled dc shunting box.

Optionally, the photovoltaic power plant provided by any one of the first aspect of the present invention further includes: an isolation transformer, wherein,

and each group of series inverters outputs alternating current electric energy to the alternating current power grid through the isolation transformer.

Optionally, the photovoltaic power plant provided by any one of the first aspect of the present invention further includes: a power generator substation comprising: at least one substation photovoltaic string, at least one substation DC combiner box, at least one centralized inverter, and a step-up transformer, wherein,

the input side of the substation direct current combiner box is connected with at least one substation photovoltaic group in series;

the output side of the substation direct current combiner box is connected with the centralized inverter;

and the centralized inverter is connected with an alternating current power grid through the step-up transformer.

Optionally, the photovoltaic power plant provided by the first aspect of the present invention further includes: a monitoring device, wherein,

the monitoring equipment is in communication connection with each group of string inverters and the centralized inverter and is used for acquiring preset operation information of each group of string inverters and the centralized inverter.

In a second aspect, the present invention provides a power generation control method applied to a string inverter in a photovoltaic power plant according to any one of the first aspect of the present invention, the method including:

calculating a reference current of a target MPPT circuit according to the reference MPPT power and the reference voltage of the target MPPT circuit; the target MPPT circuit is any one of multiple MPPT circuits of the string inverter, and the reference MPPT power is determined based on the average power output to the target MPPT circuit by a direct current shunt box connected with the target MPPT circuit;

and adjusting the actual current of the target MPPT circuit until the difference between the reference current and the actual current is within a preset current range.

Optionally, the determining the reference MPPT power of the target MPPT circuit includes:

calculating the MPPT total power output by a target direct current shunt box to a target string inverter, wherein the target direct current shunt box is a direct current shunt box connected with the target MPPT circuit, and the target string inverter is a string inverter to which the target MPPT circuit belongs;

determining the total number of MPPT circuits which are connected with the target direct current shunt box in the target string inverter;

and calculating the average value of the MPPT total power and the total quantity to obtain the reference MPPT power of the target MPPT circuit.

Optionally, the determining the reference voltage of the target MPPT circuit includes:

acquiring actual voltage of each MPPT circuit in the target string inverter, wherein the MPPT circuit is connected with the target direct current shunt box;

and determining the average value or the truncated average value of each actual voltage as the reference voltage of the target MPPT circuit.

and selecting one actual voltage from the actual voltages to be used as a reference voltage of the target MPPT circuit.

In a third aspect, the present invention provides a string inverter, comprising: a plurality of MPPT circuits, an inverter circuit, and a control module, wherein,

the output end of each MPPT circuit is respectively connected with the input end of the inverter circuit;

the output end of the inverter circuit is used as the output end of the string inverter;

the control module is respectively connected with the MPPT circuits and the control end of the inverter circuit;

the control module includes a memory and a processor, wherein the memory stores a program adapted to be executed by the processor to implement the power generation control method according to any one of the second aspects of the present invention.

In the photovoltaic power station provided by the invention, the direct current shunt box comprises one parallel input end and multiple shunt output ends, the direct current shunt box is used for shunting and outputting direct current input by the parallel input end through each shunt output end, each direct current shunt box is connected with at least one direct current combiner box, each string inverter is connected with at least one direct current shunt box, each MPPT circuit in the string inverter is connected with at least one shunt output end in the direct current shunt box, and based on the connection relation and the matched use of the direct current shunt box and the string inverter, the MPPT power shared by 1 MPPT circuit or 2 MPPT circuits in the centralized inverter in the prior art can be dispersed into more MPPT circuits, so that each string inverter can work normally.

Based on the power station structure and the connection relation among all the structural parts, in the process of reforming the photovoltaic power station by using the old centralized inverter, only the use of the centralized inverter is needed to be cancelled, the direct current shunt box and the string inverter are added on the original basis, the connection relation among all the parts is established according to the content, the reforming of the photovoltaic power station can be completed, the high-efficiency string inverter is used for replacing the low-efficiency centralized inverter, the loss in the power generation process is reduced, and therefore the problem that the overall power generation amount of the photovoltaic power station is low due to the use of the old centralized inverter in the prior art is solved, and the reforming workload is small.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of a power plant layout commonly used in photovoltaic power plants of the prior art;

FIG. 2 is a schematic diagram of a power plant layout of a photovoltaic power plant according to the present application;

FIG. 3 is a block diagram of a string inverter according to the present invention;

FIG. 4 is a schematic diagram of a plant layout for another photovoltaic power plant provided in the present application;

fig. 5 is a topology diagram of a shunt circuit in a dc shunt box according to the present invention;

FIG. 6 is a schematic diagram of a power plant layout of yet another photovoltaic power plant provided in the present application;

FIG. 7 is a flow chart of a method of generating power provided by the present application.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Optionally, referring to fig. 2, fig. 2 is a schematic diagram of a power plant layout of a photovoltaic power plant provided in the present application. The photovoltaic power station provided by the embodiment of the invention comprises: at least one dc combiner box 10, at least one dc splitter box 20, and at least one string inverter 30 including a multi-way MPPT circuit, wherein,

at least one photovoltaic string 50 is connected to the input side of each dc combiner box 10 in the photovoltaic power station, and the dc currents output by the photovoltaic strings 50 connected to the same dc combiner box 10 are finally combined to the corresponding dc combiner box 10. The number of the photovoltaic string 50 specifically connected to each dc combiner box 10 and the connection manner between the photovoltaic string 50 and the dc combiner box 10 may be determined by combining the actual scale of the photovoltaic power station according to the prior art, which is not limited in the present invention.

The dc shunting box 20 provided in the embodiment of the present invention includes a parallel input end and a plurality of shunt output ends, and the dc current input to the dc shunting box 20 through the parallel input end can be shunted and output through each shunt output end of the dc shunting box 20.

Optionally, referring to fig. 3, fig. 3 is a structural block diagram of the string inverter provided in the embodiment of the present application, the string inverter 30 provided in the embodiment of the present application is provided with multiple MPPT circuits, and certainly, in order to implement a process of inverting a direct current into an alternating current, an inverter circuit is further provided in the string inverter 30. As shown in fig. 3, the input end of each MPPT circuit in the string inverter 30 is used for receiving a direct current, the output end of each MPPT circuit is connected in parallel to the direct current input end of the inverter circuit, and the inverter circuit performs the dc-ac inversion conversion to obtain an alternating current finally. In order to realize MPPT control of each MPPT circuit and increase the output power of the photovoltaic power station as much as possible, a corresponding controller is further provided inside the string inverter 30, and the controller is connected to the control end of each MPPT circuit to control the operation process of each MPPT circuit.

Based on the above description of the structures, functions, and partial connection relationships of the dc combiner boxes 10, the dc splitter boxes 20, and the string inverter 30, in the photovoltaic power station provided in the embodiment of the present invention, the parallel input end of each dc splitter box 20 is connected to the output side of at least one dc combiner box, referring to fig. 2, two dc splitter boxes 20 are exemplarily shown, wherein two dc combiner boxes 10 are connected to the parallel input end of one dc splitter box 20, and only one dc combiner box 10 is connected to the parallel input end of the other dc splitter box 20.

Optionally, as a preferred embodiment, the dc combiner boxes connected to the dc distribution boxes 20 in the photovoltaic power station may be different from each other, and under the limitation of the connection relationship, one dc distribution box 20 in the photovoltaic power station may be correspondingly connected to one or more dc combiner boxes 10, and any one dc combiner box 10 may be connected to only one dc distribution box 20 at the same time. In the example shown in fig. 2, two dc combiner boxes are connected to one dc splitter box, and only one dc combiner box is connected to the other dc splitter box.

It should be emphasized that, for the dc splitting boxes 20 connected with two or more dc combiner boxes 10, since only one parallel input end is provided at the input side of the dc splitting box 20, in this case, the dc combiner boxes 10 connected to the same dc splitting box 20 are connected in parallel, that is, in parallel at the parallel input end of the dc splitting box 20. The parallel connection relationship between the dc combiner boxes 10 plays an important role in the photovoltaic power station provided in the embodiment of the present invention, and the following contents will be further described, which will not be detailed here.

The photovoltaic power station provided by the embodiment of the present invention may only be provided with one string inverter 30, or may be provided with a plurality of string inverters 30, and no matter how the number of string inverters 30 is specifically set, for any one string inverter 30, one dc distribution box 20 may be connected, or two or more dc distribution boxes 20 may be connected, in the embodiment shown in fig. 2, each string inverter 30 is respectively connected with one dc distribution box 20; correspondingly, referring to fig. 4, fig. 4 is a schematic diagram of a power plant layout of another photovoltaic power plant according to an embodiment of the present invention, as shown in fig. 4, one dc shunting box 20 is connected to one string of inverters 30 in the photovoltaic power plant, and two dc shunting boxes 20 are connected to the other string of inverters 30 in the photovoltaic power plant, so that, in practical applications, each string of inverters 30 may be connected to at least one dc shunting box 20 as needed. For example, the string inverter has 5 MPPT circuits, of which 3 is used to connect to the dc shunting box a and 2 is used to connect to the dc shunting box B.

However, no matter how the string inverter 30 is connected to the dc shunting boxes 20, for any one MPPT circuit in any one dc shunting box, its dc input terminal is connected to at least one shunt output terminal in the dc shunting box 20.

Optionally, as a preferred embodiment, if the dc input terminal of the MPPT circuit is connected to two or more shunt output terminals, the shunt output terminals connected to the same MPPT circuit should belong to the same dc shunt box. And the shunt output ends connected with the MPPT circuits in each group of serial inverters are different from each other.

Based on the connection restriction between the dc shunting box 20 and the string inverter 30, the group connection of the shunt output terminals in the dc shunting box 20 can be realized. Specifically, for the same way of MPPT circuit, its dc input end can connect the reposition of redundant personnel output all the way and more than, and importantly, each reposition of redundant personnel output end of connecting in the same way of MPPT circuit belongs to same dc shunt box, and the reposition of redundant personnel output end of different dc shunt boxes can not connect in the same MPPT circuit. In practical application, the dc shunting box 20 is provided with multiple paths of shunting output ends, and each MPPT circuit in the string inverter 30 has a limited capacity, and under the condition of most all the MPPT circuits, it is difficult for one path of MPPT circuit to connect all the shunting output ends in one dc shunting box 20, so that the shunting output ends of the dc shunting box 20 need to be shared by multiple paths of MPPT circuits, that is, it is equivalent to grouping the shunting output ends of the dc shunting box 20, and one group corresponds to one path of MPPT circuit, and the shunting output ends connected by each path of MPPT circuit are different from each other.

It is conceivable that, if one string inverter 30 cannot be connected to all the shunt output terminals of one dc shunt box 20, a case where one dc shunt box 20 corresponds to a plurality of string inverters 30 occurs, and such a connection is also allowable.

The ac output terminals of the groups of string inverters 30 are connected to the ac grid 40, and each group of string inverter 30 performs MPPT control based on its own MPPT circuit and outputs ac power to the ac grid 40.

Optionally, as shown in fig. 2, communication connections may also be established between the sets of string inverters 30.

Optionally, an isolation transformer (not shown in the figure) may be further disposed in the photovoltaic power station provided in the embodiment of the present invention, the output end of each group of string inverters 30 is connected to the public power grid 40 through the isolation transformer, and the mutual influence between the photovoltaic power station and the ac power grid 40 is reduced through the isolation function of the isolation transformer, especially, the influence of various ac harmonics and surge voltages existing in the ac power grid 40 on the photovoltaic power station is reduced.

Of course, the step-up transformer provided in the original photovoltaic power station may also be retained continuously, or may be removed directly, which is optional.

In summary, in the photovoltaic power station provided by the invention, through the cooperation of the dc shunt box and the string inverters, the MPPT power shared by the 1-way MPPT circuit or the 2-way MPPT circuit in the centralized inverter in the prior art can be dispersed to more MPPT circuits, so as to ensure that each string inverter can work normally.

Further, because share the power that comes to be shared by 1 way MPPT or 2 way MPPT through more ways of MPPT for the power that each way MPPT circuit needs control reduces by a wide margin, thereby reduces the degree of difficulty of MPPT control, finally reduces the risk that the parallel mismatch appears between the direct current collection flow box and the power loss that brings when taking place the parallel mismatch, helps stabilizing photovoltaic power plant's generated energy.

Further, as can be seen from the above, when a plurality of dc combiner boxes are connected to the parallel input ends of the dc splitter boxes at the same time, for the MPPT circuit in the string inverter, a part of the outputs of the dc combiner boxes are connected in parallel to the input ends of the MPPT, and the same MPPT circuit performs uniform control on the parallel partial powers, which can effectively improve the system stability compared with the prior art in which one MPPT controls one dc combiner box.

Furthermore, because the MPPT boosting unit is arranged in the string inverter, the voltage output by the string inverter can directly reach the grid-connected requirement of 400V or 480V, and therefore, the photovoltaic power station provided by the invention can be directly connected with an alternating current power grid without arranging a boosting transformer. Because the step-up transformer has certain power loss, the electric energy conversion efficiency is lower, after the step-up transformer is cancelled, the construction cost of the photovoltaic power station can be effectively reduced, and meanwhile, the power generation efficiency of the photovoltaic power station is improved.

The structure of the dc shunt box provided by the present invention is briefly introduced below, and the dc shunt box provided by the present invention includes: the box with set up the shunt circuit in the box. The box structure of the dc shunt box can be realized by referring to the box structure of the dc combiner box in the prior art, which is not limited in the present invention. Optionally, for a shunt circuit in the dc shunt box body, a specific implementation manner is provided in an embodiment of the present invention, referring to fig. 5, and fig. 5 is a topological diagram of the shunt circuit in the dc shunt box provided in the present application.

As shown in fig. 5, the shunt circuit of the dc shunt box includes a parallel input line and a multi-shunt output line. One end of the parallel input circuit is used as a parallel input end of the direct current shunt box and is connected with the direct current combiner box, the other end of the parallel input circuit is respectively connected with one end of each shunt output circuit, and the other end of each shunt output circuit is used as an output end of the direct current shunt box and is connected with an MPPT circuit in the downstream string inverter.

Optionally, the dc shunting box provided by the invention may further include a dc switch on the parallel input line, and the dc switch controls on/off of the shunting circuit to control the working state of the dc shunting box. As shown, the parallel input lines include a positive line and a negative line, and the dc switches may be respectively disposed on the positive line and the negative line of the parallel input lines. Furthermore, the direct current switch can be selected from a manual control type and an automatic control type, the specific control mode of the direct current switch is not limited, and switches capable of realizing on/off control of parallel input lines in the prior art are also optional.

In order to improve the reliability of the direct current shunt box and prevent the damage of the cable overcurrent to equipment in the photovoltaic power station under the abnormal condition, each shunt output line of the direct current shunt box is also provided with an overcurrent protection module, and when the current flowing through the line is greater than the preset current value of the overcurrent protection module, the overcurrent protection module acts to disconnect the corresponding shunt output line. Specifically, similar to the parallel input lines, each shunt output line of the shunt circuit includes a positive electrode line and a negative electrode line, and at least one of the positive electrode line and the negative electrode line is provided with an overcurrent protection module.

Optionally, the manufacturing cost of the direct current shunt box and the effectiveness of the overcurrent protection provided by the overcurrent protection module are comprehensively considered, and the overcurrent protection module can be realized by selecting a direct current fuse. In practical application, according to the power generation capacity of the photovoltaic power station, the current passing through each shunt output line is estimated, and the fusing current of the dc fuse is selected according to the current.

Optionally, when the dc shunting box operates, a large amount of current flows through an internal shunting line, and a large amount of heat is naturally generated, so that a corresponding heat dissipation measure needs to be taken for the dc shunting box. The direct current shunt box provided by the embodiment of the invention can be a forced air-cooled direct current shunt box or a natural air-cooled direct current shunt box, and the specific selection should be selected by combining the installation and use environment of the direct current shunt box and the specific heat productivity.

Optionally, referring to fig. 6, fig. 6 is a schematic diagram of a power station layout of another photovoltaic power station provided in the present application, and on the basis of the embodiment shown in fig. 2, the photovoltaic power station provided in this embodiment further includes: a generator station 60.

In this embodiment, the generator substation 60 is provided with at least one substation photovoltaic string 601, at least one substation dc combiner box 602, and a step-up transformer 604, wherein,

the input side of the substation dc combiner box 602 is connected to at least one substation photovoltaic string 601, the output side of the substation dc combiner box 602 is connected to the input side of the centralized inverter 603, and the centralized inverter 603 is connected to the ac power grid 40 via the step-up transformer 604.

From the above, it can be seen that the power generation substation 60 provided in the embodiment of the present invention is basically similar to the photovoltaic power station in the prior art, and therefore, the specific arrangement of the power generation substation 60 can be implemented with reference to the photovoltaic power station in the prior art.

In practical application, for a photovoltaic power station already built, a part of devices in the power station may be used as a power generation substation as shown in the embodiment of the present invention, and then other devices in the photovoltaic power station are modified according to the embodiment shown in fig. 2 of the present invention, so as to obtain the photovoltaic power station as shown in fig. 6.

Alternatively, on the basis of the photovoltaic power station provided in the embodiment shown in fig. 2 of the present invention, a power generation substation provided in the embodiment of the present invention is additionally constructed, and the photovoltaic power station shown in fig. 6 can be obtained in the same way.

Optionally, on the basis of any of the above embodiments, the photovoltaic power station provided by the present invention may further include a monitoring device, where the monitoring device is in communication connection with each group of string inverters and/or the centralized inverter to collect preset operation information of each group of string inverters and the centralized inverter, and feed back the obtained preset operation information to the power station control room.

Further, based on the photovoltaic power station provided by any of the above embodiments, the invention also provides a power generation control method, and the control method is applied to a string inverter in the photovoltaic power station. Alternatively, referring to fig. 7, fig. 7 is a flowchart of a power generation control method provided in an embodiment of the present invention, where the method may include:

and S100, calculating the reference current of the target MPPT circuit according to the reference MPPT power and the reference voltage of the target MPPT circuit.

As can be seen from the foregoing, the string inverters used in the embodiments of the present invention each include multiple MPPT circuits, and the same string inverter can perform MPPT control on each MPPT set by itself, and of course, the control methods are the same, that is, the control method provided in the embodiments of the present invention. Based on this, the target MPPT circuit described in the embodiment of the present invention is specified as any one of the multiple MPPT circuits included in the string inverter to which the power generation control method proposed in the embodiment of the present invention is applied.

Further, for convenience of describing the power generation control method provided in the present embodiment, the string inverter to which the target MPPT circuit belongs is referred to as a target string inverter, and the dc distribution box to which the target MPPT circuit is connected is referred to as a target dc distribution box.

Optionally, to calculate the reference current of the target MPPT circuit, first, the reference MPPT power of the target MPPT circuit and the reference voltage of the target MPPT circuit should be determined.

Specifically, the MPPT total power output from the target dc shunt box to the target string inverter is calculated first. As can be seen from the foregoing, for the target dc shunting box, there is a possibility that the target dc shunting box corresponds to multiple MPPT circuits in the target string inverter, and even there is a possibility that the target dc shunting box has a connection relationship with other string inverters other than the target string inverter.

Optionally, the MPPT powers of the MPPT circuits in the target string inverter and connected to the target dc shunt box may be calculated respectively, and then the sum of the MPPT powers is calculated, which is the MPPT total power.

When calculating the MPPT power of each MPPT circuit having a connection relation with the target dc shunt box in the target string inverter, the MPPT circuit may calculate the MPPT power by using an actual voltage and an actual current of each MPPT circuit itself, or may specify a reference voltage, and then each MPPT circuit calculates the MPPT power of itself by using the reference voltage and the actual current of itself. On the premise of not exceeding the core thought range of the invention, any method capable of calculating the MPPT power of the MPPT circuit and further obtaining the MPPT total power is optional and also belongs to the protection scope of the invention.

After obtaining the MPPT total power output by the target dc shunt box to the target string inverter, the total number of MPPT circuits in the target string inverter, which have a connection relationship with the target dc shunt box, needs to be further determined. It is conceivable that, in practical applications, the connection relationship among the electrical devices in the photovoltaic power station is already determined, and therefore, the total number of the MPPT circuits mentioned herein may be stored in the controller of the string inverter in advance, and certainly, the total number of the MPPT circuits may also be determined according to the actual conditions of the MPPT circuits in the string inverter.

And finally, calculating the average value of the total MPPT power and the total MPPT power to obtain the reference MPPT power of the target MPPT circuit.

According to the calculation process, the reference MPPT power of the target MPPT circuit is actually an average value of the MPPT powers of the MPPT circuits in the target string inverter, which have a connection relationship with the target dc shunt box.

For the reference voltage of the target MPPT circuit, which has been mentioned slightly above, the following is detailed:

optionally, the actual voltage of each MPPT circuit in the target string inverter, which has a connection relationship with the target dc shunt box, is obtained first. Then, calculating an average value or a truncated average value of the obtained multiple actual voltages, and taking the obtained average value or the truncated average value as a reference voltage of the target MPPT circuit, and certainly, the obtained average value or the truncated average value can also be used as a reference voltage used for calculating the total power of the MPPT;

or selecting any one of the obtained actual voltages as a reference voltage of the target MPPT circuit;

alternatively, the actual voltage of the target MPPT circuit may be directly used as the reference voltage in the embodiment of the present invention.

After the reference MPPT power and the reference voltage of the target MPPT circuit are obtained, the reference MPPT power is divided by the reference voltage, and then the reference current of the target MPPT circuit can be obtained.

And S110, adjusting the actual current of the target MPPT circuit until the difference between the reference current and the actual current is within a preset current range.

And after the parameters are obtained, closed-loop control can be performed on the target MPPT circuit, the reference current is taken as a standard value, the actual current of the target MPPT circuit is adjusted until the difference between the reference current and the actual current is within a preset current range, and the MPPT control process is finished.

In summary, since the input terminals of the MPPT circuits are equivalently in a parallel state (parallel points are located at parallel input terminals of the dc shunt box), the power generation control method provided in the embodiment of the present invention performs MPPT control on the MPPT circuits based on the parallel state, so that currents output by the MPPT circuits connected to the same dc shunt box are substantially the same (both are near a reference current), thereby implementing cable current sharing control between the dc shunt box and the string inverter, effectively reducing the probability of parallel mismatch of the photovoltaic strings connected to the dc shunt box side, and contributing to improving the operation stability of the photovoltaic power station.

Optionally, the present invention further provides a string inverter, including: a plurality of MPPT circuits, an inverter circuit, and a control module, wherein,

the output end of each MPPT circuit is connected with the input end of the inverter circuit;

the control module comprises a memory and a processor, wherein the memory stores programs suitable for the processor to execute so as to realize the power generation control method provided by any one of the above embodiments of the invention.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A photovoltaic power plant, characterized in that it comprises at least one DC combiner box, at least one DC splitter box and at least one string inverter comprising a multi-way MPPT circuit, wherein,

2. The photovoltaic power plant of claim 1 wherein the dc combiner boxes to which each of the dc splitter boxes are connected are different from each other.

3. The photovoltaic power plant of claim 1 wherein the split outputs connected to the same MPPT circuit belong to the same dc split box and the split outputs connected to each MPPT circuit are different from each other.

4. The photovoltaic power plant of claim 1 wherein the dc shunt box comprises: a box body and a shunt circuit arranged in the box body, wherein,

5. The photovoltaic power plant of claim 4 wherein the parallel input line is provided with a DC switch.

6. The photovoltaic power plant of claim 4 wherein the split output lines comprise positive and negative lines, wherein,

7. The photovoltaic power plant of claim 6 wherein the over-current protection module comprises a DC fuse.

8. The photovoltaic power plant of any one of claims 1 to 7 wherein the dc distribution box comprises a forced air-cooled dc distribution box or a natural air-cooled dc distribution box.

9. The photovoltaic power plant of any one of claims 1-7 further comprising: an isolation transformer, wherein,

10. The photovoltaic power plant of claim 1 further comprising: a power generator substation comprising: at least one substation photovoltaic string, at least one substation DC combiner box, at least one centralized inverter, and a step-up transformer, wherein,

11. The photovoltaic power plant of claim 10 further comprising: a monitoring device, wherein,

12. A power generation control method applied to the string inverter in the photovoltaic power plant according to any one of claims 1 to 11, the method comprising:

13. The power generation control method as set forth in claim 12, wherein determining the reference MPPT power of the target MPPT circuit includes:

14. The power generation control method as set forth in claim 13, wherein the process of determining the reference voltage of the target MPPT circuit includes:

15. The power generation control method as set forth in claim 13, wherein the process of determining the reference voltage of the target MPPT circuit includes:

16. A string inverter, comprising: a plurality of MPPT circuits, an inverter circuit, and a control module, wherein,

the control module includes a memory and a processor, wherein the memory stores a program adapted to be executed by the processor to implement the power generation control method according to any one of claims 12 to 15.