CN111463830A - Local area power grid networking method and application system thereof - Google Patents
Local area power grid networking method and application system thereof Download PDFInfo
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Abstract
The local power grid networking method is applied to a photovoltaic inversion system comprising a plurality of string-type inverters and is executed under the condition that a low-voltage side switch or a high-voltage side switch of a grid-connected transformer in the photovoltaic inversion system is not conducted; then, starting each group of string inverters in the photovoltaic inversion system to run in a current source mode in a grid-connected inversion mode, and after an alternating-current low-voltage side network is established, performing thermal debugging on each device, which needs to be subjected to thermal debugging, on the low-voltage side of the photovoltaic inversion system; and then solved prior art and waited for the problem of the time delay that main electric network power transmission led to.
Description
Technical Field
The invention relates to the technical field of control, in particular to a local area power grid networking method and an application system thereof.
Background
After the power station is built, the inverter, the box-type transformer, the metering cabinet, the main transformer, the communication equipment and the like in the power station need to be subjected to thermal debugging so as to ensure that all the equipment has no fault and can normally operate.
In the process of performing thermal debugging on each device, current must be introduced into the devices in the power station that need to be subjected to thermal debugging. Because the early construction of the power station consumes a great deal of time, the time reserved for the thermal debugging is very limited; if the power station live debugging is carried out after the main power grid is powered on, once any equipment fails, the project with a short construction period may miss the time point of the installation, and huge loss is caused.
Disclosure of Invention
Therefore, the local area power grid networking method and the application system thereof are provided to solve the problem that the existing thermal debugging can be performed only after the main power grid is powered on, and the faulty equipment is prone to missing the time point of installing the faulty equipment.
In order to achieve the above purpose, the embodiments of the present invention provide the following technical solutions:
the application discloses in a first aspect, a local area network networking method, which is applied to a photovoltaic inverter system comprising a plurality of string inverters, and the local area network networking method is executed under the condition that a low-voltage side switch or a high-voltage side switch of a grid-connected transformer in the photovoltaic inverter system is not switched on:
at least one group of series inverters in the photovoltaic inversion system is started in an independent inversion mode, operates in a voltage source mode, and establishes alternating current low-voltage side voltage of the photovoltaic inversion system;
and the rest serial inverters in the photovoltaic inversion system are started in a grid-connected inversion mode, run in a current source mode, and establish an alternating current low-voltage side network of the photovoltaic inversion system.
Optionally, in the local area network networking method, the independent inversion mode is as follows: and the corresponding group of series inverters control the series inverters to work in a constant alternating voltage output state according to the preset voltage reference value of the series inverters.
Optionally, in the local area grid networking method, the grid-connected inversion mode is as follows: and the corresponding group of series inverters control the mode of outputting active power or reactive power according to a certain power factor or power instruction according to the received instruction.
Optionally, in the local area power grid networking method, if the main circuit of the string inverter includes an inverter unit and a DCDC conversion unit, at least one string inverter in the photovoltaic inverter system is started in an independent inverter mode, and operates in a form of a voltage source, and establishes an ac low-voltage side voltage of the photovoltaic inverter system, including:
judging whether the current state meets the starting condition of the corresponding group of serial inverters;
if the current state meets the starting condition of the inverter, the corresponding group of series inverters controls the DCDC conversion unit of the inverter to start, and the internal direct-current bus voltage is established;
and the corresponding group of series inverters controls the own inversion unit to start in the independent inversion mode.
Optionally, in the local area power grid networking method, if the main circuit of the string inverter only includes an inverter unit, at least one string inverter in the photovoltaic inverter system is started in an independent inverter mode and operates in the form of a voltage source, and an ac low-voltage side voltage of the photovoltaic inverter system is established, including:
judging whether the current state meets the starting condition of the corresponding group of serial inverters;
and if the current state meets the self starting condition, the corresponding group of serial inverters directly controls the self inversion unit to start in the independent inversion mode.
Optionally, in the method for networking the local area power grid, the step of judging whether the current state meets the starting condition of the corresponding string inverter includes:
the corresponding group of series inverters judges whether the PV voltage received by the corresponding group of series inverters is larger than the corresponding lowest starting voltage;
if the PV voltage received by the inverter is larger than the corresponding lowest starting voltage, the corresponding group of series inverters judge whether the current AC low-voltage side voltage is smaller than the AC low-voltage threshold value;
and if the current alternating-current low-voltage side voltage is smaller than the alternating-current low-voltage threshold value, judging that the current state meets the self starting condition by the corresponding group of series inverters.
Optionally, in the method for networking the local area power grid, after the corresponding string inverter determines whether the PV voltage received by the corresponding string inverter is greater than the corresponding lowest starting voltage, the method further includes:
and if the PV voltage received by the inverter is less than or equal to the corresponding lowest starting voltage, returning to the step that the corresponding group of series inverters judges whether the PV voltage received by the inverter is greater than the corresponding lowest starting voltage.
Optionally, in the method for networking the local area power grid, after the corresponding string inverter determines whether the current ac low-voltage side voltage is less than the ac low-voltage threshold, the method further includes:
and if the current alternating current low-voltage side voltage is larger than or equal to the alternating current low-voltage threshold, starting each group of string type inverters in the photovoltaic inversion system in a grid-connected inversion mode, operating in a current source mode, and establishing the alternating current low-voltage side network.
Optionally, in the local area power grid networking method, if the main circuit of the string-type inverter group includes an inverter unit and a DCDC conversion unit, each remaining string-type inverter group in the photovoltaic inverter system is started in a grid-connected inverter mode, and operates in a current source mode to establish the ac low-voltage side network, including:
judging whether the current state meets grid-connected conditions or not by the corresponding group of series inverters;
if the current state meets the grid-connected condition, the corresponding group of series inverters controls the DCDC conversion unit of the corresponding group of series inverters to start, and the internal direct-current bus voltage is established;
and controlling the self inverter unit by the corresponding group of series inverters to start grid-connected operation in the grid-connected inverter mode.
Optionally, in the local power grid networking method, if the main circuit of the string inverter includes only an inverter unit, the remaining string inverters in the photovoltaic inverter system are started in a grid-connected inverter mode, run in a current source mode, and establish the ac low-voltage side network, where the method includes:
judging whether the current state meets grid-connected conditions or not by the corresponding group of series inverters;
and if the current state meets the grid-connected condition, the corresponding group of series inverters directly controls the own inverter unit to start grid-connected operation in the grid-connected inverter mode.
Optionally, in the method for networking the local area power grid, the step of judging whether the current state meets the grid-connected condition by the corresponding string-type inverter includes:
the corresponding group of series inverters judges whether the PV voltage received by the corresponding group of series inverters is larger than the corresponding lowest starting voltage;
if the PV voltage received by the inverter is larger than the corresponding lowest starting voltage, the corresponding group of series inverters judge whether the current AC low-voltage side voltage meets the grid-connected requirement;
and if the current alternating-current low-voltage side voltage meets the grid-connected requirement, judging that the current state meets the grid-connected condition by the corresponding group of series inverters.
Optionally, in the method for networking the local area power grid, after the corresponding string inverter determines whether the PV voltage received by the corresponding string inverter is greater than the corresponding lowest starting voltage, the method further includes:
and if the PV voltage received by the inverter is less than or equal to the corresponding lowest starting voltage, returning to the step of executing the corresponding group of series inverters to judge whether the PV voltage received by the inverter is greater than the corresponding lowest starting voltage.
Optionally, in the method for networking the local area power grid, after the corresponding string inverter determines whether the current ac low-voltage side voltage meets the grid connection requirement, the method further includes:
and if the current alternating-current low-voltage side voltage does not meet the grid-connected requirement, returning to the step of executing the corresponding group of string inverters to judge whether the PV voltage received by the corresponding group of string inverters is greater than the corresponding lowest starting voltage.
Optionally, in the local area grid networking method, before at least one string inverter in the photovoltaic inverter system is started in an independent inverter mode and operated in the form of a voltage source to establish an ac low-voltage side voltage of the photovoltaic inverter system, the method further includes:
a monitoring system in the photovoltaic inversion system issues a starting instruction to at least one string inverter in the photovoltaic inversion system, so that the inverter is started in an independent inversion mode;
and before each remaining string-type inverter in the photovoltaic inverter system is started in a grid-connected inverter mode, and is operated in a current source mode to establish the alternating-current low-voltage side network, the method further includes:
and the monitoring system issues a starting instruction to each remaining group of series inverters in the photovoltaic inversion system to start the series inverters in a grid-connected inversion mode.
Optionally, in the local area grid networking method, after at least one string inverter in the photovoltaic inverter system is started in an independent inverter mode and operated in the form of a voltage source, and an ac low-voltage side voltage of the photovoltaic inverter system is established, the method further includes:
the corresponding group of serial inverters judges whether the voltage of the alternating current low-voltage side reaches a grid-connected rated voltage;
and if the voltage of the alternating-current low-voltage side reaches the grid-connected rated voltage, the corresponding group of series inverters send feedback information of the establishment of the alternating-current voltage to the monitoring system.
The second aspect of the present application discloses a photovoltaic inverter system, includes: the photovoltaic grid-connected inverter comprises a plurality of string-type inverters, a plurality of photovoltaic string groups, a grid-connected transformer, a data acquisition unit and a monitoring system;
the direct current side of each string-type inverter is connected with the corresponding photovoltaic string;
after the alternating current sides of the group of series inverters are connected in parallel, the group of series inverters are connected with the monitoring system through the data collector and are also connected with a power grid through the low-voltage side switch, the grid-connected transformer and the high-voltage side switch in sequence;
the monitoring system is configured to control the monitoring system and each string inverter to perform any local area grid networking method disclosed in the first aspect.
Optionally, in the above photovoltaic inverter system, the main circuit of the string inverter includes only an inverter unit, or includes the inverter unit and a plurality of DCDC conversion units located at a front stage of the inverter unit.
The local power grid networking method is applied to a photovoltaic inversion system comprising a plurality of string-type inverters and is executed under the condition that a low-voltage side switch or a high-voltage side switch of a grid-connected transformer in the photovoltaic inversion system is not conducted, firstly, at least one string-type inverter in the photovoltaic inversion system is started in an independent inversion mode and runs in the form of a voltage source to establish alternating current low-voltage side voltage of the photovoltaic inversion system, so that power supply for thermal debugging is provided, and the grid in the prior art is replaced to realize thermal debugging and power transmission; then, starting each remaining string-type inverter in the photovoltaic inversion system in a grid-connected inversion mode, operating in a current source mode, and establishing an alternating-current low-voltage side network, wherein each device on the low-voltage side of the photovoltaic inversion system, which needs to be subjected to thermal debugging, can be subjected to thermal debugging; and then solved prior art and waited for the problem of the time delay that main electric network power transmission led to.
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 embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 to fig. 8 are eight flowcharts of a local area network networking method provided in an embodiment of the present application;
fig. 9 is a schematic structural diagram of a photovoltaic inverter system according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, 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 invention.
The embodiment of the application provides a local area power grid networking method, which is used for solving the problem that the existing hot debugging can be carried out only after a main power grid is powered on, and the problem that faulty equipment misses a rush-installation time point easily is solved.
Referring to fig. 1, the local area grid networking method is applied to a photovoltaic inverter system (as shown in fig. 9, including at least two string inverters) including a plurality of string inverters, and is performed when a low-voltage side switch (such as an ac low-voltage switch shown in fig. 9) or a high-voltage side switch (such as an ac high-voltage switch shown in fig. 9) of a grid-connected transformer in the photovoltaic inverter system is not turned on, and the method mainly includes the following steps:
s101, at least one string type inverter in the photovoltaic inversion system is started in an independent inversion mode, and the string type inverter runs in a voltage source mode to establish alternating current low-voltage side voltage of the photovoltaic inversion system.
The independent inversion mode is that the group string type inverter controls the group string type inverter to work in a constant alternating voltage output state according to a preset voltage reference value. Under the condition of no alternating voltage, the group of string inverters are started by energy on the direct current side of the group of string inverters, and alternating current is output by inversion, so that voltage is generated on the alternating current low-voltage side of the system.
The voltage source is in a form that the group string type inverter outputs stable alternating voltage according to a preset alternating voltage instruction (including amplitude and frequency), so that the system can establish alternating low-voltage side voltage.
Specifically, the ac low-voltage side voltage refers to a voltage on an ac low-voltage side of the photovoltaic inverter system.
And S102, starting the rest serial inverters in the photovoltaic inversion system in a grid-connected inversion mode, operating in a current source mode, and establishing an alternating current low-voltage side network of the photovoltaic inversion system.
The grid-connected inversion mode is that the corresponding group of series inverters control the series inverters to work in a constant alternating voltage output state according to the received instruction.
In practical application, the string inverter can work in a constant alternating voltage output state according to an instruction of an upper computer in a photovoltaic system.
Under the condition that the alternating voltage meets the working range of the group string type inverters, the group string type inverters output voltages with the same frequency and phase as the alternating voltage.
Specifically, the P (U) mode and the Q (U) mode both belong to control modes in a grid-connected inversion mode.
The p (u) mode is a process in which the group string inverter dynamically controls the active power output by the group string inverter according to the magnitude of the alternating voltage and a preset curve or a received external instruction.
The mode Q (U) is a process that the group string type inverter dynamically adjusts the reactive power output by the group string type inverter according to the size of the alternating voltage and a preset curve or a received external instruction.
The current source mode is a mode that the group string type inverter is connected with a stable alternating current power grid according to the input power, and then outputs power with certain current to feed the power grid.
Specifically, the alternating-current low-voltage side network means that electric energy flows among equipment on the alternating-current low-voltage side of the photovoltaic inverter system to form an electric energy flowing network.
Based on the above principle, in the local power grid networking method provided in this embodiment, under the condition that a low-voltage side switch or a high-voltage side switch of a grid-connected transformer in a photovoltaic inverter system is not turned on, at least one string-type inverter in the photovoltaic inverter system is started in an independent inverter mode and runs in the form of a voltage source to establish an alternating-current low-voltage side voltage of the photovoltaic inverter system, so that power supply for thermal debugging is provided, and a power grid in the prior art is replaced to realize thermal debugging and power transmission; then, starting each remaining string-type inverter in the photovoltaic inversion system in a grid-connected inversion mode, operating in a current source mode, and establishing an alternating-current low-voltage side network, wherein each device on the low-voltage side of the photovoltaic inversion system, which needs to be subjected to thermal debugging, can be subjected to thermal debugging; and then solved prior art and waited for the problem of the time delay that main electric network power transmission led to.
It is worth to be noted that, in the prior art, there is a scheme for performing thermal debugging on equipment by additionally arranging a diesel engine in a photovoltaic inverter system, and although the thermal debugging before power transmission of a power grid can be realized, the cost is high, and the operation of a diesel generator is complex. In the local area power grid networking method provided by the embodiment, at least one string-type inverter in the photovoltaic inverter system replaces a power grid through the step S102, so that a power supply for hot debugging is provided, and hot debugging of each device in the photovoltaic inverter system is not required in a mode of simulating the power grid by using a diesel engine mobile power supply, so that complicated operations caused by adding the diesel engine mobile power supply for hot debugging are reduced, the hot debugging of the photovoltaic inverter system is simpler and more convenient, and no extra hot debugging cost is required.
It is also worth mentioning that although there is also a method of local area network networking for two centralized inverters in the prior art, this prior method is not suitable for multiple string inverters; the local area power grid networking method provided by the application can be suitable for a plurality of group series inverters.
Optionally, referring to fig. 2, in another embodiment provided by the present application, before performing step S101, starting at least one string inverter in the photovoltaic inverter system in an independent inverter mode, and operating in the form of a voltage source, and establishing an ac low-voltage side voltage of the photovoltaic inverter system, the method further includes:
s201, a monitoring system in the photovoltaic inversion system issues a starting instruction to at least one string inverter in the photovoltaic inversion system, so that the inverter is started in an independent inversion mode.
Specifically, in practical applications, the monitoring system may control the data collector to send the start instruction to the corresponding string inverter by sending the control instruction to the data collector, or the data collector may forward the start instruction sent by the monitoring system to the corresponding string inverter.
In practical applications, referring to fig. 2 as well, the method may be implemented by a monitoring system in the photovoltaic inverter system through communication with each string inverter, specifically, the specific process of the method is as follows:
s201, a monitoring system in the photovoltaic inversion system issues a starting instruction to at least one string inverter in the photovoltaic inversion system, so that the inverter is started in an independent inversion mode.
Specifically, referring to fig. 7, in practical application, the monitoring system may issue a control instruction to the data collector (i.e., L ogger shown in fig. 7) to control the data collector to issue a start instruction to the corresponding string inverter, or may also forward the start instruction issued by the monitoring system to the corresponding string inverter through the data collector.
After step S201, step S101 is executed, at least one string inverter in the photovoltaic inverter system is started in an independent inverter mode, and is operated in a voltage source manner, so as to establish an ac low-voltage side voltage of the photovoltaic inverter system. After step S101, step S301 is executed.
S301, the corresponding group of serial inverters judges whether the voltage of the alternating current low-voltage side reaches the grid-connected rated voltage.
The string inverter in step S301 is the same as or the same as the string inverter in step S101. I.e. the subject performing step S301 is the same as the subject performing step S101.
The grid-connected rated voltage is the requirement that the alternating-current voltage output by the group string type inverter meets the grid-connected rated voltage.
If the ac low-voltage side voltage reaches the grid-connected rated voltage, step S302 is performed.
And S302, the corresponding group of serial inverters sends feedback information of the completion of the establishment of the alternating voltage to the monitoring system.
After receiving the feedback information of the ac voltage establishment completion sent by the string inverters, the monitoring system may issue a start instruction to each remaining string inverter in the photovoltaic inverter system to start the string inverter in the grid-connected inverter mode, that is, step S202 described below.
S202, the monitoring system issues a starting instruction to each remaining string-type inverter in the photovoltaic inversion system to start the string-type inverters in the grid-connected inversion mode.
It should be noted that, in practical application, after step S202, step S102 is executed, and each remaining string inverter in the photovoltaic inverter system is started in a grid-connected inverter mode, and runs in a current source mode to establish an ac low-voltage side network of the photovoltaic inverter system, that is, step S202 is executed before step S102.
In this embodiment, the photovoltaic inverter system issues a start instruction to at least one string inverter in the photovoltaic inverter system through a monitoring system in the photovoltaic inverter system, so that the at least one string inverter is started in an independent inverter mode, and after it is determined that the ac voltage is established, a start instruction is issued to each remaining string inverter in the photovoltaic inverter system, so that the at least one string inverter is started in a grid-connected inverter mode, that is, the photovoltaic inverter system can automatically establish a grid of the system through the monitoring system in the photovoltaic inverter system.
On the basis of the above embodiments, in another embodiment provided by the present application, please refer to fig. 3 (taking the example shown on fig. 1), if the main circuit of the string-type inverter includes an inverter unit and a DCDC conversion unit connected in parallel with a plurality of output terminals located at a front stage of the inverter unit, step S101 is executed, at least one string-type inverter in the photovoltaic inverter system is started in an independent inverter mode and operated in a voltage source mode, and a specific process of establishing an ac low-voltage side voltage of the photovoltaic inverter system is as follows:
s401, judging whether the current state meets the starting condition of the corresponding group of serial inverters.
If the current state satisfies the self-start condition, that is, step S402 is executed.
S402, the corresponding group of series inverters controls the DCDC conversion unit to start, and internal direct-current bus voltage is established.
And S403, controlling the self inverter unit to start in an independent inverter mode by the corresponding group of serial inverters.
In practical applications, if the main circuit of the string inverter only includes an inverter unit, please refer to fig. 4 (also shown on the basis of fig. 1 as an example), step S101 is executed, at least one string inverter in the photovoltaic inverter system is started in an independent inverter mode and operated in a voltage source mode, and the specific process of establishing the ac low-voltage side voltage of the photovoltaic inverter system is as follows:
s501, judging whether the current state meets the starting condition of the corresponding group of serial inverters.
If the current state satisfies the self-start condition, step S502 is executed.
S502, the corresponding group of serial inverters directly controls the own inversion unit to start in an independent inversion mode.
Based on fig. 3 or fig. 4 (taking the example shown in fig. 3 as an example), in practical applications, please refer to fig. 5, the process of executing step S401 and the corresponding string inverter to determine whether the current state satisfies the self-start condition, or, the process of executing step S501 and the corresponding string inverter to determine whether the current state satisfies the self-start condition is:
s601, judging whether the PV voltage received by the corresponding string type inverter is larger than the corresponding lowest starting voltage or not.
The minimum starting voltage is the minimum voltage requirement which needs to be met by the self direct current side of the group string type inverter when the self direct current side of the group string type inverter starts the self and outputs an alternating current mode through the self direct current side energy under the condition that no alternating current voltage exists on the self alternating current side.
Because each group of series inverters is internally provided with the DCDC conversion unit, the PV voltage received by the group of series inverters needs to be judged whether to be greater than the corresponding lowest starting voltage or not every day in the starting process of the group of series inverters. If the PV voltage received by the DCDC conversion unit is greater than the corresponding minimum starting voltage, step S602 is executed, and it is determined that the DCDC conversion unit in the string-type inverter operates in the bypass state or the boost state according to the actual condition of the PV voltage. Specifically, if the PV voltage is higher, the DCDC conversion unit in the string-type inverter is controlled to operate in a bypass state; if the PV voltage is lower, the DCDC conversion unit in the control group string type inverter operates in a boosting state.
S602, the corresponding group of serial inverters judges whether the current alternating current low-voltage side voltage is smaller than an alternating current low-voltage threshold value.
The alternating current low-voltage threshold value is a voltage value range in which the string-type inverter can realize starting and self-starting according to the alternating current voltage of the alternating current low-voltage side of the string-type inverter.
If the current ac low-voltage side voltage is smaller than the ac low-voltage threshold, step S603 is executed.
And S603, judging that the current state meets the self starting condition by the corresponding group of serial inverters.
It should be noted that, after determining whether the PV voltage of the string inverter is greater than the corresponding minimum starting voltage, it cannot be directly determined whether the current state of the string inverter satisfies the starting condition of the string inverter itself, and it needs to further determine whether the current ac low-voltage side voltage of the string inverter is smaller than the ac low-voltage threshold, so as to avoid adverse effects on the string inverter caused by the independent inversion mode starting when the PV voltage is greater than the corresponding minimum starting voltage and the current ac low-voltage side voltage is greater than the ac low-voltage threshold.
Optionally, in practical applications, referring to fig. 5 as well, after the step S601 is executed, and the corresponding group of string inverters determines whether the PV voltage received by the corresponding group of string inverters is greater than the corresponding lowest starting voltage, if the PV voltage received by the corresponding group of string inverters is less than or equal to the corresponding lowest starting voltage, the method further includes: and returning to the step of judging whether the PV voltage received by the corresponding string inverter is greater than the corresponding lowest starting voltage, namely returning to the step S601.
It should be noted that after determining that the PV voltage received by the PV generator is equal to or lower than the corresponding lowest starting voltage, the process may return to step S601 directly, or may return to step S601 after a certain period of time.
In this embodiment, after the determination in step S601 is performed, if the condition is not satisfied, the step is still performed again, whether the PV voltage received by the string-type self-generator is greater than the corresponding minimum starting voltage can be determined in real time, and when it is determined that the PV voltage received by the self-generator is greater than the corresponding minimum starting voltage, the subsequent steps are performed in time, so that unnecessary time consumption in the power grid self-building process is reduced.
Optionally, in practical applications, referring to fig. 5, after step S602 is executed, and the corresponding group of string inverters determine whether the current ac low-voltage side voltage is less than the ac low-voltage threshold, if the current ac low-voltage side voltage is greater than or equal to the ac low-voltage threshold, the method further includes: and executing the step that each remaining string-type inverter in the photovoltaic inversion system is started in a grid-connected inversion mode, runs in a current source mode, and establishes an alternating current low-voltage side network, namely executing the step S102.
After the determination of step S602 is performed, if the current ac low-voltage side voltage is greater than or equal to the ac low-voltage threshold, it indicates a request for establishing an ac low-voltage side network by the current ac low-voltage side voltage of the string-type inverter, and step S102 may be directly performed.
On the basis of the above embodiments, in another embodiment provided in the present application, please refer to fig. 6 (taking the example shown on fig. 1), if the main circuit of the group of string inverters includes an inverter unit and a plurality of DCDC conversion units connected in parallel at output ends located at a front stage of the inverter unit, step S102 is executed, the remaining group of string inverters in the photovoltaic inverter system are started in a grid-connected inverter mode, and run in a current source manner, and a specific process of establishing an ac low-voltage side network of the photovoltaic inverter system is as follows:
s701, judging whether the current state meets grid-connected conditions or not by the corresponding group of serial inverters.
And the grid connection condition is that the current state of the group-string type inverter meets the condition of being merged into the power grid.
If the current state meets the grid-connection condition, step S702 is executed.
S702, the corresponding group of series inverters controls the DCDC conversion unit to start, and internal direct-current bus voltage is established.
Specifically, the DCDC conversion unit of the group string inverter is controlled to start, and the process of establishing the internal dc bus voltage is the same as that in the prior art, which can be referred to in the prior art and is not described in detail herein.
And S703, controlling the self inverter unit by the corresponding group of serial inverters to start grid-connected operation in a grid-connected inverter mode.
Similarly, the group-string inverter controls the own inverter unit to start grid-connected operation in a grid-connected inverter mode, which is also the same as that in the prior art, and the specific process can be referred to in the prior art, which is not described in detail herein.
In practical application, if the main circuit of the string-type inverter only includes an inverter unit, please refer to fig. 7, step S102 is executed, and the remaining string-type inverters in the photovoltaic inverter system are started in a grid-connected inverter mode and run in a current source mode, and the specific process of establishing the ac low-voltage side network of the photovoltaic inverter system is as follows:
s801, judging whether the current state meets grid-connected conditions or not by the corresponding group of serial inverters.
If the current state meets the grid-connection condition, step S802 is executed.
And S802, directly controlling the self inverter unit by the corresponding group of serial inverters to start grid-connected operation in the grid-connected inverter mode.
In practical applications, please refer to fig. 8 (which is shown by taking the example of fig. 6 as an example), step S701 is executed, and the corresponding string inverter determines whether the current state meets the grid-connected condition, or step S801 is executed, and the specific process of determining whether the current state meets the grid-connected condition by the corresponding string inverter is as follows:
s901, the corresponding group of series inverters judges whether the PV voltage received by the corresponding group of series inverters is larger than the corresponding lowest starting voltage.
Specifically, the relevant description of step S901 can refer to step S601, and is not described herein again.
If the PV voltage received by the PV module is greater than the corresponding minimum start-up voltage, step S902 is performed.
And S902, judging whether the current alternating current low-voltage side voltage meets the grid-connected requirement by the corresponding group of series inverters.
Specifically, grid connection requires that the voltage output by the string inverter can be incorporated into the grid and fed to the grid.
And if the current alternating-current low-voltage side voltage meets the grid-connection requirement, executing step S903.
And S903, judging that the current state meets grid-connected conditions by the corresponding group of series inverters.
The group-string type inverter can be fed to the power grid by being incorporated into the power grid only when the PV voltage is greater than the lowest starting voltage of the group-string type inverter and the current AC low-voltage side voltage of the group-string type inverter meets the grid-connection requirement. Therefore, if the current ac low-voltage side voltage of the inverter is directly fed to the grid to feed the grid only by separately judging that the current ac low-voltage side voltage of the inverter meets the grid-connection requirement, a situation that the grid-connection fails due to the fact that the PV voltage received by the inverter cannot be normally started and operated due to the fact that the PV voltage received by the inverter is not greater than the corresponding minimum starting voltage may occur.
In a practical application, referring to fig. 8, after the step S901 is executed, and the corresponding string inverter determines whether the PV voltage received by the corresponding string inverter is greater than the corresponding minimum starting voltage, if the PV voltage received by the corresponding string inverter is less than or equal to the corresponding minimum starting voltage, the method further includes: and returning to the step of executing the corresponding group of string inverters to judge whether the PV voltage received by the corresponding group of string inverters is greater than the corresponding lowest starting voltage, that is, returning to the step S901.
It should be noted that, after determining that the PV voltage received by the receiver is less than or equal to the corresponding lowest starting voltage, the process may return to perform step S901 directly, or after a period of time, the process may return to perform step S901.
In this embodiment, after the determination in step S901 is performed, if the condition is not satisfied, the step is still performed again, whether the PV voltage received by the string-type PV itself is greater than the corresponding minimum starting voltage can be determined in real time, and when it is determined that the PV voltage received by the string-type PV itself is greater than the corresponding minimum starting voltage, the subsequent steps are performed in time, so that unnecessary time consumption in the power grid self-building process is reduced.
Referring to fig. 8, in practical applications, after the step S902 is executed and the corresponding string inverter determines whether the current ac low-voltage side voltage meets the grid-connection requirement, if the current ac low-voltage side voltage does not meet the grid-connection requirement, the method further includes: and returning to the step of executing the corresponding group of string inverters to judge whether the PV voltage received by the corresponding group of string inverters is greater than the corresponding lowest starting voltage, that is, returning to the step S901.
It should be noted that after the current ac low-voltage side voltage is judged not to have reached the grid connection requirement, the step S901 may be directly executed, or the step S901 may be executed after a period of time is set.
In this embodiment, after the step S902 is executed to determine that the current ac low-voltage side voltage does not reach the grid-connection requirement, the step of determining whether the PV voltage received by the photovoltaic inverter system is greater than the corresponding minimum starting voltage is executed again, so that it can be ensured that the photovoltaic inverter system executes the subsequent grid self-building step in time after the PV voltage received by the photovoltaic inverter system is greater than the corresponding minimum starting voltage and the current ac low-voltage side voltage reaches the grid-connection requirement.
Fig. 3, fig. 5, fig. 6, and fig. 8 show a specific implementation process of the method when the main circuits of the string inverters all include an inverter unit and a DCDC conversion unit, that is, one or more string inverters start the DCDC conversion unit first, and then start the inverter unit, so that the corresponding inverter unit starts in an independent inverter mode, and continuously operates in a voltage source mode to establish an ac voltage; and then other groups of series inverters are started according to a grid-connected mode of the grid-connected inverter, work in the states of P (U) and Q (U), and operate according to the form of a current source.
Fig. 4 and fig. 7 show a specific implementation process of the method when the main circuit of the string-type inverter only includes the inverter unit, and after the current state of one or more string-type inverters meets the start condition, the one or more string-type inverters directly control the inverter unit to start in an independent inverter mode, and continuously operate in the form of a voltage source to establish an ac voltage; and then other groups of series inverters are started according to a grid-connected mode of the grid-connected inverter, work in the states of P (U) and Q (U), and operate according to the form of a current source.
Another embodiment of the present application further provides a photovoltaic inverter system, please refer to fig. 9, which mainly includes a plurality of string-type inverters (illustrated in fig. 9 by taking # 1 string-type inverter and # 2 string-type inverter as examples), a plurality of photovoltaic string (illustrated in fig. 9 by taking # 1 photovoltaic array and # 2 photovoltaic array as examples), a grid-connected transformer, a data collector (i.e., L ogger illustrated in fig. 9), and a monitoring system.
It should be noted that fig. 9 only shows a case corresponding to a photovoltaic inverter system including 2 group string inverters, but in practical applications, the number of the group string inverters may be any number; the number of the group string inverters is not particularly limited, and all the group string inverters belong to the protection scope of the application.
And the direct current side of each group of series inverters is respectively connected with the corresponding photovoltaic group in series. The dc side of the string inverter is the side of the string inverter receiving dc power, i.e. the side of the string inverter connected to the pv array as shown in fig. 9.
The group-string inverter comprises a plurality of DCDC conversion units inside, and the input end of each conversion unit is connected with a photovoltaic group string or a plurality of photovoltaic group strings connected in parallel. Therefore, the direct current side of each string inverter is respectively connected with a plurality of photovoltaic strings; that is, each photovoltaic array shown in fig. 9 includes a plurality of photovoltaic string.
In practical applications, the main circuit of the series inverter may only include an inverter unit, or a plurality of DCDC conversion units with parallel output terminals may be further disposed at a preceding stage of the inverter unit, depending on a specific application environment, and all of them are within the protection scope of the present application.
After the alternating current sides of the group string inverters are connected in parallel, the group string inverters are connected with a monitoring system through a data acquisition unit and are also connected with a power grid through a low-voltage side switch, a grid-connected transformer and a high-voltage side switch in sequence.
The side where the group string type inverter, the data collector and the low-voltage side relay are connected is the alternating current low-voltage side of the photovoltaic inversion system; and one side of the high-voltage side relay connected with the power grid is an alternating current high-voltage side of the photovoltaic inverter system.
The ac low-voltage side switch may specifically include a low-voltage circuit breaker and a low-voltage load switch; the high-side switch may specifically comprise a high-voltage circuit breaker and a high-voltage load switch.
The monitoring system is used for controlling the local power grid and each group of series inverters to execute the local power grid networking method provided by the corresponding embodiments of the above-mentioned fig. 1 to fig. 8 through the data acquisition unit, so as to complete the establishment of the local power grid.
Based on the local area power grid networking method and the photovoltaic inverter system shown in fig. 9, the photovoltaic inverter system provided by the application can execute the local area power grid networking method shown in the embodiment corresponding to fig. 1 to 8, so that the power grid self-construction of the photovoltaic inverter system is completed; that is, the photovoltaic inverter system can perform thermal debugging on low-voltage equipment such as a photovoltaic module, a string inverter, low-voltage monitoring equipment (such as a data acquisition unit and a monitoring system) and the like in the photovoltaic inverter system when a high-voltage side relay is not switched on, and the thermal debugging can be performed after the construction of each equipment in the low-voltage section is completed, so that the thermal debugging efficiency is improved; and this hot debugging process is gone on when high-pressure side relay does not close a floodgate, and photovoltaic inverter system does not insert the high-voltage electric wire netting, and then makes the process of hot debugging safer.
Features described in the embodiments in the present specification may be replaced with or combined with each other, and the same and similar portions among the embodiments may be referred to each other, and each embodiment is described with emphasis on differences from other embodiments. In particular, the system or system embodiments are substantially similar to the method embodiments and therefore are described in a relatively simple manner, and reference may be made to some of the descriptions of the method embodiments for related points. The above-described system and system embodiments are only illustrative, wherein the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
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 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.
It is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
Claims (17)
1. A local area network networking method is applied to a photovoltaic inverter system comprising a plurality of string-type inverters, and is performed under the condition that a low-voltage side switch or a high-voltage side switch of a grid-connected transformer in the photovoltaic inverter system is not conducted:
at least one group of series inverters in the photovoltaic inversion system is started in an independent inversion mode, operates in a voltage source mode, and establishes alternating current low-voltage side voltage of the photovoltaic inversion system;
and the rest serial inverters in the photovoltaic inversion system are started in a grid-connected inversion mode, run in a current source mode, and establish an alternating current low-voltage side network of the photovoltaic inversion system.
2. The local area power grid networking method according to claim 1, wherein the independent inversion mode is: and the corresponding group of series inverters control the series inverters to work in a constant alternating voltage output state according to the preset voltage reference value of the series inverters.
3. The local area power grid networking method according to claim 1, wherein the grid-connected inversion mode is: and the corresponding group of series inverters control the mode of outputting active power or reactive power according to a certain power factor or power instruction according to the received instruction.
4. The method according to claim 1, wherein if the main circuit of the string-type inverter includes an inverter unit and a DCDC conversion unit, at least one string-type inverter in the pv inverter system is started in an independent inverter mode and operated in a voltage source mode to establish an ac low-side voltage of the pv inverter system, the method comprising:
judging whether the current state meets the starting condition of the corresponding group of serial inverters;
if the current state meets the starting condition of the inverter, the corresponding group of series inverters controls the DCDC conversion unit of the inverter to start, and the internal direct-current bus voltage is established;
and the corresponding group of series inverters controls the own inversion unit to start in the independent inversion mode.
5. The local area power grid networking method according to claim 4, wherein if the main circuit of the string-type inverter group only includes an inverter unit, at least one string-type inverter group in the photovoltaic inverter system is started up in an independent inverter mode and operated in a voltage source mode, and an alternating low-voltage side voltage of the photovoltaic inverter system is established, including:
judging whether the current state meets the starting condition of the corresponding group of serial inverters;
and if the current state meets the self starting condition, the corresponding group of serial inverters directly controls the self inversion unit to start in the independent inversion mode.
6. The local area power grid networking method according to claim 4 or 5, wherein the step of judging whether the current state meets the starting condition of the corresponding string inverter comprises the following steps:
the corresponding group of series inverters judges whether the PV voltage received by the corresponding group of series inverters is larger than the corresponding lowest starting voltage;
if the PV voltage received by the inverter is larger than the corresponding lowest starting voltage, the corresponding group of series inverters judge whether the current AC low-voltage side voltage is smaller than the AC low-voltage threshold value;
and if the current alternating-current low-voltage side voltage is smaller than the alternating-current low-voltage threshold value, judging that the current state meets the self starting condition by the corresponding group of series inverters.
7. The local area power grid networking method of claim 6, wherein after the corresponding string inverter determines whether the PV voltage received by itself is greater than the corresponding lowest starting voltage, the method further comprises:
and if the PV voltage received by the inverter is less than or equal to the corresponding lowest starting voltage, returning to the step that the corresponding group of series inverters judges whether the PV voltage received by the inverter is greater than the corresponding lowest starting voltage.
8. The local area power grid networking method of claim 6, wherein after the corresponding string inverter determines whether the current ac low-voltage side voltage is less than the ac low-voltage threshold, the method further comprises:
and if the current alternating current low-voltage side voltage is larger than or equal to the alternating current low-voltage threshold, starting each group of string type inverters in the photovoltaic inversion system in a grid-connected inversion mode, operating in a current source mode, and establishing the alternating current low-voltage side network.
9. The method according to claim 1, wherein if the main circuit of the string inverters includes an inverter unit and a DCDC converter unit, each remaining string inverter in the pv inverter system is started in a grid-connected inverter mode, and operates in a current source mode to establish the ac low-voltage side network, including:
judging whether the current state meets grid-connected conditions or not by the corresponding group of series inverters;
if the current state meets the grid-connected condition, the corresponding group of series inverters controls the DCDC conversion unit of the corresponding group of series inverters to start, and the internal direct-current bus voltage is established;
and controlling the self inverter unit by the corresponding group of series inverters to start grid-connected operation in the grid-connected inverter mode.
10. The method according to claim 1, wherein if the main circuit of the string inverters only includes an inverter unit, each remaining string inverter in the pv inverter system is started in a grid-connected inverter mode, and operates in a current source mode to establish the ac low-voltage side network, including:
judging whether the current state meets grid-connected conditions or not by the corresponding group of series inverters;
and if the current state meets the grid-connected condition, the corresponding group of series inverters directly controls the own inverter unit to start grid-connected operation in the grid-connected inverter mode.
11. The local area power grid networking method according to claim 9 or 10, wherein the step of judging whether the current state meets the grid-connection condition by the corresponding string-type inverter comprises the steps of:
the corresponding group of series inverters judges whether the PV voltage received by the corresponding group of series inverters is larger than the corresponding lowest starting voltage;
if the PV voltage received by the inverter is larger than the corresponding lowest starting voltage, the corresponding group of series inverters judge whether the current AC low-voltage side voltage meets the grid-connected requirement;
and if the current alternating-current low-voltage side voltage meets the grid-connected requirement, judging that the current state meets the grid-connected condition by the corresponding group of series inverters.
12. The method according to claim 11, wherein after the corresponding string inverter determines whether the PV voltage received by itself is greater than the corresponding lowest starting voltage, the method further comprises:
and if the PV voltage received by the inverter is less than or equal to the corresponding lowest starting voltage, returning to the step of executing the corresponding group of series inverters to judge whether the PV voltage received by the inverter is greater than the corresponding lowest starting voltage.
13. The local area power grid networking method according to claim 11, wherein after the corresponding string inverter determines whether the current ac low-voltage side voltage meets the grid connection requirement, the method further comprises:
and if the current alternating-current low-voltage side voltage does not meet the grid-connected requirement, returning to the step of executing the corresponding group of string inverters to judge whether the PV voltage received by the corresponding group of string inverters is greater than the corresponding lowest starting voltage.
14. The local area power grid networking method according to any one of claims 1 to 5, 7 to 10, and 12 to 13, wherein before the at least one string inverter in the pv inverter system is started in the independent inverter mode and operated in the form of a voltage source to establish the ac low-side voltage of the pv inverter system, the method further comprises:
a monitoring system in the photovoltaic inversion system issues a starting instruction to at least one string inverter in the photovoltaic inversion system, so that the inverter is started in an independent inversion mode;
and before each remaining string-type inverter in the photovoltaic inverter system is started in a grid-connected inverter mode, and is operated in a current source mode to establish the alternating-current low-voltage side network, the method further includes:
and the monitoring system issues a starting instruction to each remaining group of series inverters in the photovoltaic inversion system to start the series inverters in a grid-connected inversion mode.
15. The local area power grid networking method according to claim 14, wherein after at least one string inverter in the pv inverter system is started in an independent inverter mode and operated in a voltage source mode to establish an ac low-side voltage of the pv inverter system, the method further comprises:
the corresponding group of serial inverters judges whether the voltage of the alternating current low-voltage side reaches a grid-connected rated voltage;
and if the voltage of the alternating-current low-voltage side reaches the grid-connected rated voltage, the corresponding group of series inverters send feedback information of the establishment of the alternating-current voltage to the monitoring system.
16. A photovoltaic inverter system, comprising: the photovoltaic grid-connected inverter comprises a plurality of string-type inverters, a plurality of photovoltaic string groups, a grid-connected transformer, a data acquisition unit and a monitoring system;
the direct current side of each string-type inverter is connected with the corresponding photovoltaic string;
after the alternating current sides of the group of series inverters are connected in parallel, the group of series inverters are connected with the monitoring system through the data collector and are also connected with a power grid through the low-voltage side switch, the grid-connected transformer and the high-voltage side switch in sequence;
the monitoring system is used for controlling the monitoring system and each group of string inverters to execute the local area power grid networking method according to any one of claims 1 to 15 through the data acquisition unit.
17. The pv inversion system according to claim 16, wherein the main circuit of the string inverter includes only the inversion unit, or includes the inversion unit and a plurality of DCDC conversion units located at a front stage of the inversion unit.
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