CN110943472A - Photovoltaic grid-connected system, control method and device - Google Patents
Photovoltaic grid-connected system, control method and device Download PDFInfo
- Publication number
- CN110943472A CN110943472A CN201811109868.XA CN201811109868A CN110943472A CN 110943472 A CN110943472 A CN 110943472A CN 201811109868 A CN201811109868 A CN 201811109868A CN 110943472 A CN110943472 A CN 110943472A
- Authority
- CN
- China
- Prior art keywords
- switch
- voltage
- transformer
- low
- voltage side
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
- H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
- H02M5/10—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using transformers
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
Abstract
The application provides a photovoltaic grid-connected system, a control method and a device, wherein the system is additionally provided with a small-capacity second boosting transformer, and the second boosting transformer is connected in parallel with two ends of a branch formed by connecting a first boosting transformer and a main switch in series and is used for pre-exciting the first boosting transformer. The second step-up transformer has the same phase difference and transformation ratio as the first step-up transformer, and therefore, the high-voltage side voltage of the first step-up transformer is equal to the high-voltage side voltage (i.e., the grid voltage) of the second step-up transformer. Therefore, the system does not need to collect the voltage of a power grid, so that the cost of a medium-voltage (or high-voltage) voltage sensor is saved; moreover, a sampling and communication connecting line of a voltage sensor is not required to be arranged, so that the complexity of a system connecting line is reduced; furthermore, the arrangement of sampling and communication connecting lines in the system is reduced, so that the faults caused by the damage of the connecting lines are reduced, and the reliability of the system is improved.
Description
Technical Field
The invention belongs to the technical field of photovoltaic power generation, and particularly relates to a photovoltaic grid-connected system, a control method and a device.
Background
Grid connection refers to the connection of a power generation system to a public power grid, and a photovoltaic grid connection system refers to the connection of a photovoltaic power generation system to a public power grid.
For a photovoltaic power station or a distributed grid-connected power generation system, the direct current energy of a photovoltaic array needs to be inverted by an inversion system and then fed to a medium-voltage or high-voltage power grid through a step-up transformer. The moment that the step-up transformer is directly connected to a power grid can generate excitation impact, and then impact current is generated. The impact current can impact key devices such as a step-up transformer, a medium-high voltage switch and the like in the photovoltaic grid-connected system, and if the impact current is too large, the key devices are damaged. In addition, the electric energy quality of the power grid is also affected by the overlarge impact current.
Disclosure of Invention
In view of this, the present invention provides a photovoltaic grid-connected system, a control method and a device, so as to solve the problem that in the conventional scheme, a boost transformer is connected to a power grid to instantly generate an impulse current, and the impulse current causes impact on key devices in the system, thereby causing damage to the key devices.
In a first aspect, the present application provides a photovoltaic grid-connected system, including: the device comprises an inversion unit, an inversion switch, a first boosting transformer, a main switch, a second boosting transformer, a first switch, a second switch and a control unit, wherein the phase difference and the transformation ratio of the second boosting transformer and the first boosting transformer are the same, and the second boosting transformer pre-excites the first boosting transformer;
the direct current end of the inversion unit is connected with a direct current power supply, and the alternating current end of the inversion unit is connected with the low-voltage side of the first boosting transformer through the inversion switch;
the high-voltage side of the first booster transformer is connected with one end of the main switch, and the other end of the main switch is connected with a power grid;
one end of the first switch is connected with the low-voltage side of the first boosting transformer, and the other end of the first switch is connected with the low-voltage side of the second boosting transformer;
one end of the second switch is connected with the high-voltage side of the second booster transformer, and the other end of the second switch is connected with the power grid;
the control unit is used for controlling the first switch and the second switch to be closed before grid connection, and controlling the main switch to be closed and controlling the first switch and the second switch to be opened when the low-voltage side voltage of the first boosting transformer is detected.
Optionally, the number of the inversion units and the number of the inversion switches are both N, and N is an integer greater than 1;
the direct current end of each inversion unit is connected with a direct current power supply, the alternating current end of each inversion unit is connected with one end of one inversion switch, and the other end of each inversion switch is connected with the low-voltage side of the first boosting transformer after being connected in parallel.
Optionally, the inverter switch, the first switch and the second switch adopt any one of a combination of a circuit breaker and a load switch plus a fuse.
In a second aspect, the present application further provides another photovoltaic grid-connected system, including: the system comprises an inversion unit, an inversion switch, a third boosting transformer, a main switch, a fourth boosting transformer, a first switch and a control unit;
the direct current end of the inverter unit is connected with a direct current power supply, and the alternating current end of the inverter unit is connected with the low-voltage side of the third boosting transformer through the inverter switch;
the high-voltage side of the third booster transformer is connected with one end of the main switch, and the other end of the main switch is connected with a power grid;
one end of the first switch is connected with the high-voltage side of the fourth step-up transformer, and the other end of the first switch is connected with the power grid;
the control unit is used for controlling the first switch to be closed before grid connection, acquiring the voltage of the low-voltage side of the fourth boosting transformer, and calculating according to the voltage of the low-voltage side, the voltage of the third boosting transformer and the parameter of the fourth boosting transformer to obtain the preset voltage of the low-voltage side of the third boosting transformer;
and the inversion unit is used for pre-exciting the third boosting transformer until the voltage of the low-voltage side of the third boosting transformer reaches the preset voltage, and directly or indirectly controlling the main switch to be switched on.
Optionally, the number of the inversion units and the number of the inversion switches are both N, and N is an integer greater than 1;
and the direct current end of each inversion unit is respectively connected with a direct current power supply, the alternating current end of each inversion unit is respectively connected with one end of one inversion switch, and the other end of each inversion switch is connected in parallel and then connected with the low-voltage side of the third step-up transformer.
Optionally, the inverter switch, the first switch and the second switch adopt any one of a circuit breaker and a load switch plus a fuse.
In a third aspect, the present application further provides a photovoltaic grid-connected control method, which is applied to the photovoltaic grid-connected system described in any one of the possible implementation manners of the first aspect, and the method includes:
before grid connection, the second switch and the first switch are controlled to be closed, so that the second boosting transformer performs pre-excitation on the first boosting transformer;
and when the voltage of the low-voltage side of the first boosting transformer is detected, controlling the main switch to be closed, controlling the first switch and the second switch to be disconnected, and controlling the inversion switch to be closed.
In a fourth aspect, the present application further provides another photovoltaic grid-connected control method, which is applied to the photovoltaic grid-connected system according to any possible implementation manner of the second aspect, and the method includes:
before grid connection, the first switch is controlled to be closed, and the voltage of the low-voltage side of the fourth boosting transformer is obtained;
calculating to obtain a preset voltage of the low-voltage side of the third step-up transformer according to the low-voltage side voltage, the parameters of the third step-up transformer and the parameters of the fourth step-up transformer;
controlling at least one inverter switch to be switched on, and pre-exciting the third step-up transformer to enable the low-voltage side voltage of the third step-up transformer to reach the preset voltage;
and when the voltage of the low-voltage side of the third step-up transformer reaches a preset voltage, controlling the main switch to be closed.
In a fifth aspect, the present application provides a photovoltaic grid-connected control device, which is applied to the photovoltaic grid-connected system according to any one of the possible implementation manners of the first aspect, where the device includes:
the first control module is used for controlling the second switch and the first switch to be closed before grid connection so as to enable the second boosting transformer to be pre-excited for the first boosting transformer;
and the second control module is used for controlling the main switch to be closed, controlling the first switch and the second switch to be disconnected and controlling the inversion switch to be closed after the voltage of the low-voltage side of the first boosting transformer is detected.
In a sixth aspect, the present application provides a photovoltaic grid-connected control device, which is applied to the photovoltaic grid-connected system according to any one of the possible implementation manners of the second aspect, where the device includes:
the first control module is used for controlling the first switch to be closed before grid connection;
the acquisition module is used for acquiring the low-voltage side voltage of the fourth boosting transformer;
the calculation module is used for calculating and obtaining the preset voltage of the low-voltage side of the third boosting transformer according to the low-voltage side voltage, the parameters of the third boosting transformer and the parameters of the fourth boosting transformer;
the second control module is used for controlling at least one inverter switch to be switched on and pre-exciting the third boosting transformer so as to enable the voltage of the low-voltage side of the third boosting transformer to reach the preset voltage;
and the third control module is used for controlling the main switch to be closed after the voltage of the low-voltage side of the third boosting transformer reaches a preset voltage.
Compared with the prior art, the technical scheme provided by the invention has the following advantages: and a second step-up transformer is additionally arranged and is connected in parallel with two ends of a branch formed by the first step-up transformer and the main switch in series and used for pre-exciting the first step-up transformer. After the first boosting transformer is pre-excited, the main switch is closed, and switches at two ends of the second boosting transformer are simultaneously disconnected, so that grid connection of the photovoltaic grid-connected system is realized. Because the transformation ratio and the phase difference of the second boosting transformer and the first boosting transformer are the same, namely the high-voltage side voltage of the first boosting transformer is equal to the high-voltage side voltage (namely the power grid voltage) of the second boosting transformer, the system does not need a special medium-voltage (or high-voltage) voltage sensor, and the cost of the medium-voltage (or high-voltage) voltage sensor is saved; moreover, a sampling and communication connecting line of a voltage sensor is not required to be arranged, so that the complexity of a system connecting line is reduced; furthermore, the arrangement of sampling and communication connecting lines in the system is reduced, so that the faults caused by the damage of the connecting lines are reduced, and the reliability of the system is improved.
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 introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a schematic block diagram of a photovoltaic grid-connected system provided in an embodiment of the present application;
fig. 2 is a schematic block diagram of another photovoltaic grid-connected system provided in an embodiment of the present application;
fig. 3 is a flowchart of a photovoltaic grid-connected control method provided by the embodiment of the present application;
fig. 4 is a flowchart of another photovoltaic grid-connected control method provided in the embodiment of the present application;
fig. 5 is a block diagram of a photovoltaic grid-connected control device provided in an embodiment of the present application;
fig. 6 is a block diagram of another photovoltaic grid-connected control device provided in the embodiment of the present application.
Detailed Description
Before the grid connection of the photovoltaic grid connection system, the booster transformer can be pre-excited by the energy of the direct current side of the inverter unit, so that the voltage with the same amplitude and the same phase as the medium-voltage or high-voltage power grid is established on the high-voltage side of the booster transformer, the overcurrent impact caused in the moment of inputting the power grid is reduced, and the service life of key devices and the reliability of the power grid are improved.
According to the traditional scheme, the output voltage of the step-up transformer needs to be acquired through three connecting wires, the voltage of a medium-voltage or high-voltage power grid is acquired through the other three connecting wires, and when the two voltages are consistent, namely the pre-excitation of the step-up transformer is successful, the main switch is closed. The system relates to connecting wires of a medium-high voltage transformer, related sampling communication and the like, the wiring of the system is complex, and meanwhile, the safety of the system is reduced; moreover, the cost of the medium-high voltage transformer is high.
In order to solve the problem that the high-voltage transformer in the photovoltaic grid-connected system generates impact current instantly when being connected to the grid, the step-up transformer can be pre-excited by the energy of the direct current side of the inverter unit before being connected to the grid, so that the voltage with the same amplitude and the same phase as the medium-voltage or high-voltage power grid is established on the high-voltage side of the step-up transformer, overcurrent impact caused instantly when the power grid is connected is reduced, and the service life of a key device and the reliability of the power grid are improved.
During pre-excitation of the step-up transformer, it is usually necessary to collect voltages at both sides of the main switch, i.e. the grid voltage and the output voltage of the step-up transformer; when the two voltages are detected to be consistent, the pre-excitation of the step-up transformer is successful, and then the main switch is closed, so that the impact on key devices in a photovoltaic grid-connected system at the moment of grid connection is reduced. The grid voltage belongs to medium voltage or high voltage, and a medium voltage (or high voltage) voltage transformer is expensive, so that the cost of the photovoltaic grid-connected system is high. In addition, since the medium-voltage (or high-voltage) voltage transformer belongs to a medium-voltage (or high-voltage) device, the medium-voltage (or high-voltage) voltage transformer needs to be arranged at an interval with a low-voltage device, and a sampling signal is not suitable for long-distance transmission, a sampling control unit needs to be additionally arranged on the side of the voltage transformer. Processing a voltage sampling result through the sampling control unit, wherein the processing result needs to be sent to a system control unit in the photovoltaic grid-connected system so that the control unit controls the state of a main switch; therefore, a communication connection line between the sampling control unit and the system control unit needs to be added, which increases the complexity of the system.
The application provides a photovoltaic grid-connected system, and this system can realize the pre-excitation to step-up transformer under the condition of the voltage sensor that need not gather step-up transformer's output voltage and grid voltage, makes step-up transformer's output voltage and grid voltage amplitude, phase place the same, has reduced system cost. Meanwhile, the system does not need to sample the middle and high voltage, so that an additional sampling control unit is not needed, and the cost and the complexity of the system are further reduced
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, 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 some, but not all, embodiments of the present invention. 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.
Referring to fig. 1, a schematic block diagram of a photovoltaic grid-connected system according to an embodiment of the present disclosure is shown, where the system shown in this embodiment includes N inverter units, N inverter switches, a first step-up transformer 1, a main switch K1, a second step-up transformer 2, a first switch K2, a second switch K3, and a control unit 3; wherein N is a positive integer.
In other embodiments of the present application, a value of N may be 1, and a working principle of the photovoltaic grid-connected system when the value of N is equal to 1 is the same as that of the photovoltaic grid-connected system when the value of N is greater than 2, so that the present embodiment will focus on the photovoltaic grid-connected system when N is greater than or equal to 2.
As shown in fig. 1, the dc end of each inverter unit is connected to a dc power supply PV, the ac end of each inverter unit is connected to one end of an inverter switch, and the other end of the inverter switch is connected in parallel and then connected to the low-voltage side of the first step-up transformer 1;
for example, the ac terminal of inverter unit #1 is connected to one terminal of inverter switch #1, and the ac terminal of inverter unit # N is connected to one terminal of inverter switch # N; the other ends of the inverter switches #1 to # N are connected in parallel and then connected to the low-voltage side of the first step-up transformer 1.
The inverter unit is used for converting the direct current output by the direct current power supply into alternating current and supplying the alternating current to the first boosting transformer 1 for boosting.
The high-voltage side of the first step-up transformer 1 is connected with one end of a main switch K1, and the other end of K1 is connected with a power grid.
The second step-up transformer 2 is connected in parallel to two ends of a series branch formed by the first step-up transformer and the main switch K1 in series through a first switch K2 and a second switch K3.
As shown in fig. 1, one end of the first switch K2 is connected to the low-voltage side winding of the first step-up transformer 1, and the other end of K2 is connected to the low-voltage side winding of the second step-up transformer 2; one end of the second switch K3 is connected to the high-voltage side winding of the second step-up transformer 2, and the other end of the switch K3 is connected to the grid.
In the present embodiment, the first step-up transformer 1 and the second step-up transformer 2 are of the same group, that is, the first step-up transformer 1 and the second step-up transformer 2 have the same phase difference and the same transformation ratio. Further, the second step-up transformer 2 is used to pre-excite the first step-up transformer 1, and the energy required to pre-excite the first step-up transformer 1 depends mainly on the no-load loss of the first step-up transformer 1, and therefore, the capacity of the second step-up transformer 2 needs to be greater than or equal to the no-load loss of the first step-up transformer 1. The no-load loss of the first step-up transformer 1 is usually several thousandth of its own capacity, and the capacity of the second step-up transformer 2 is small, so the cost of the second step-up transformer 2 is low.
In the embodiment of the application, the inverter switch and the main switch K1 can be both circuit breakers; the first switch K2 and the second switch K3 may be a circuit breaker, or a combination of a load switch and a fuse.
In one embodiment of the present application, the control unit 3 is used to directly detect and control the closed/open states of K1, K2, and K3. In other embodiments of the present application, the control unit 3 may communicate with an inverter unit, which may detect and control the on/off states of K1, K2, and K3 through the control unit.
In a possible implementation manner of the present application, in order to improve the integration level of the system and improve the convenience of system maintenance, the control unit 3 may be integrated in a system control unit of the photovoltaic grid-connected system, that is, a control unit for detecting and controlling the on-off states of K1, K2, and K3 is not required to be additionally added, so that the cost and the system complexity are further reduced.
The working process of the photovoltaic grid-connected system provided by the embodiment is as follows:
before the photovoltaic grid-connected system is put into grid connection, the inverter switches connected with the inverter units are in a disconnected state, and meanwhile, the main switch K1 is also in a disconnected state; then, the first switch K2 and the second switch K3 are closed, and at this time, the high-voltage side of the second step-up transformer 2 is connected to the grid, and the low-voltage side of the second step-up transformer 2 is connected to the low-voltage side of the first step-up transformer 1. Therefore, the voltage on the high-voltage side of the second step-up transformer 2 is equal to the grid voltage, and the voltage on the low-voltage side of the first step-up transformer 1 is equal to the voltage on the low-voltage side of the second step-up transformer 2.
Since the transformation ratio and the phase difference between the first step-up transformer 1 and the second step-up transformer 2 are the same, when the low-voltage side voltage of the first step-up transformer 1 is the same as the low-voltage side voltage of the second step-up transformer 2, the high-voltage side voltage of the first step-up transformer 1 is also the same as the high-voltage side voltage of the second step-up transformer 2. Based on the principle, pre-excitation is carried out on the first boosting transformer 1 by using the second boosting transformer 2; when the voltage on the low-voltage side of the first step-up transformer 1 is detected, indicating that the pre-excitation process of the first step-up transformer 1 is finished, closing the main switch K1, and simultaneously, opening K2 and K3 to complete the connection of the first step-up transformer 1 to the power grid. And finally, closing the inverter switches connected with the inverter units to complete the subsequent normal grid connection process.
According to the photovoltaic grid-connected system provided by the embodiment, the second boosting transformer which has the same transformation ratio and phase difference with the first boosting transformer is additionally arranged; the second step-up transformer is connected in parallel with two ends of a branch circuit formed by the first step-up transformer and the main switch in series; when the first switch and the second switch are closed, the high-side voltage of the second step-up transformer is equal to the grid voltage, and the low-side voltage of the first step-up transformer is equal to the low-side voltage of the second step-up transformer. The transformation ratio and the phase difference of the second step-up transformer are the same as those of the first step-up transformer, so that the high-voltage side voltage of the low-voltage side voltage after being boosted by the first step-up transformer is equal to the high-voltage side voltage (namely, the power grid voltage) of the second step-up transformer, and the pre-excitation process of the first step-up transformer is completed. And then, closing the main switch, and simultaneously disconnecting the first switch and the second switch to realize grid connection of the photovoltaic grid-connected system. The system pre-excites the first boosting transformation through the second boosting transformer, a medium-voltage (or high-voltage) voltage transformer is not needed, and the cost of a medium-voltage (or high-voltage) acquisition device is saved; moreover, a connecting wire of the voltage transformer is not required to be arranged, so that the complexity of the system connecting wire is reduced. Furthermore, the arrangement of sampling and communication connecting lines in the system is reduced, so that the faults caused by the damage of the connecting lines are reduced, and the reliability of the system is improved.
Referring to fig. 2, a schematic block diagram of another photovoltaic grid-connected system according to an embodiment of the present application is shown, where the photovoltaic grid-connected system described in this embodiment collects a grid voltage by using another step-up transformer.
As shown in fig. 2, the system includes N inverter units, N inverter switches, a third step-up transformer 11, a fourth step-up transformer 12, a main switch K4, a third switch K5, and a control unit 13; wherein N is a positive integer.
The working process of the photovoltaic grid-connected system when N is 1 is the same as that when N is greater than or equal to 2, and this embodiment is described by taking N as an example.
As shown in fig. 2, the dc end of each inverter unit is connected to a dc power supply, the ac end of each inverter unit is connected to one end of an inverter switch, and the other end of the inverter switch is connected in parallel and then connected to the low-voltage side winding of the third step-up transformer 11. For example, the ac terminal of inverter unit #1 is connected to one terminal of inverter switch #1, and the ac terminal of inverter unit # N is connected to one terminal of inverter switch # N; the other end of each inverter switch is connected in parallel to the low-voltage side winding of the third step-up transformer 11.
The high-voltage side winding of the third step-up transformer 11 is connected with one end of a main switch K4, and the other end of K4 is connected with a power grid.
The high-voltage side winding of the fourth step-up transformer 12 is connected to the grid through a third switch K5, wherein the high-voltage side winding of the fourth step-up transformer 12 is connected to one end of K5, and the other end of K5 is connected to the grid.
In the embodiment of the application, the inverter switch and the main switch K4 can be both circuit breakers; the third switch K5 can be a circuit breaker or a combination of a load switch and a fuse.
In one embodiment of the present application, the detection and control of the closed/open states of K1, K2, and K3 may be detected directly by the control unit 13. In other embodiments of the present application, the control unit 3 may communicate with an inverter unit, which may detect and control the on/off states of K1, K2, and K3 through the control unit.
In a possible implementation manner of the present application, in order to improve the integration level of the system and improve the convenience of system maintenance, the control unit 13 may be integrated into a system control unit of the photovoltaic grid-connected system, that is, a control unit for detecting and controlling the on-off states of K4 and K5 is not required to be additionally added, so that the cost and the system complexity are further reduced.
The working process of the photovoltaic grid-connected system provided by the embodiment is as follows:
before the photovoltaic grid-connected system is put into grid connection, each inverter switch is in a disconnected state, and meanwhile, the main switch K4 is also in a disconnected state; then, the third switch K5 is closed; at this time, the high-voltage side of fourth step-up transformer 12 is connected to the grid, i.e., the high-voltage side voltage of fourth step-up transformer 12 is equal to the grid voltage. The control unit may obtain the low-voltage side voltage of the fourth step-up transformer 12 collected by the low-voltage transformer, calculate the amplitude of the grid voltage according to the collected low-voltage side voltage and the transformation ratio of the transformer, and calculate the phase of the grid voltage by using the phase difference of the fourth step-up transformer 12.
Then, the inverting unit calculates, according to the calculated grid voltage and the transformation ratio of the third step-up transformer 13, a voltage amplitude that the low-voltage side of the third step-up transformer 13 should reach when the high-voltage side reaches the grid voltage, and calculates, according to the phase difference of the third step-up transformer, a phase corresponding to the low-voltage, where the voltage that the low-voltage side should reach is referred to as a preset voltage. Then, at least one inversion switch is closed, and an inversion unit connected with the inversion switch in a closed state pre-excites the third step-up transformer 11 by using the energy of a direct-current power supply connected with a direct-current side;
in the process that the inversion unit pre-excites the third step-up transformer 11, the inversion unit can sample the voltage at the low-voltage side of the third step-up transformer 11 through the control unit 13 to confirm that the amplitude and the phase of the voltage output by the inversion unit are matched with the amplitude and the phase of the preset voltage; after a certain time delay, the main switch K4 is closed, and simultaneously, the third switch K5 is opened, so that the pre-excitation process of the third step-up transformer is completed. And after pre-excitation is completed, the inversion unit completes the subsequent grid connection process.
In addition, the fourth step-up transformer 12 can be used as a system distribution transformer after completing the pre-excitation process of the third step-up transformer 11, so as to meet the power supply requirements of some low-voltage loads.
According to the photovoltaic grid-connected system provided by the embodiment, the high-voltage side of the fourth step-up transformer is connected with the power grid, and then the amplitude and the phase of the voltage of the power grid are obtained by collecting the amplitude and the phase of the voltage of the low-voltage side of the fourth step-up transformer. And determining a preset voltage which should be reached by the low-voltage side of the third step-up transformer according to the amplitude and the phase of the voltage of the power grid, pre-exciting the third step-up transformer by at least one inversion unit by using the energy of the direct-current power supply, and closing the main switch to complete grid connection when the voltage of the low-voltage side of the third step-up transformer reaches the preset voltage. According to the system, the grid voltage is collected through the fourth booster transformer, a high-voltage transformer with high use cost is not needed, and a connecting wire of the voltage transformer is not needed, so that the complexity of the connecting wire of the system is reduced, and the reliability of the system is further improved.
On the other hand, corresponding to the photovoltaic grid-connected system, the application also provides an embodiment of a grid-connected control method of the photovoltaic grid-connected system.
As shown in fig. 3, a flowchart of a photovoltaic grid-connected control method according to an embodiment of the present application is shown, where the method is applied to the system shown in fig. 1, and as shown in fig. 3, the method may include the following steps:
and S110, controlling the first switch K2 and the second switch K3 to be closed so that the second step-up transformer performs pre-excitation on the first step-up transformer.
As shown in fig. 1, after K2 and K3 are closed, the voltage on the high side of the second step-up transformer is equal to the grid voltage, and the voltage on the low side of the first step-up transformer is equal to the voltage on the low side of the second step-up transformer. Since the transformation ratio and the phase difference of the first step-up transformer and the second step-up transformer are the same, the high-voltage side voltage of the first step-up transformer is equal to the high-voltage side voltage of the second step-up transformer, i.e., the grid voltage. Thereby completing the pre-excitation operation of the first step-up transformer.
S120, detecting whether voltage exists on the low-voltage side of the first boosting transformer or not, and if so, executing S130; otherwise, after the preset time interval, returning to execute S120.
And S130, controlling the main switch to be closed, and controlling the first switch and the second switch to be opened.
And after pre-excitation of the first step-up transformer is completed, controlling the main switch to be closed so as to enable the first step-up transformer to be connected to the grid.
And S140, controlling the inverter switch to be closed so as to complete grid connection of the photovoltaic grid-connected system.
And after the inversion switch is controlled to be closed, the grid connection process of the inversion unit is completed.
According to the photovoltaic grid-connected control method provided by the embodiment, the second boosting transformer is used for pre-exciting the first boosting transformer, a medium-voltage (or high-voltage) voltage sensor is not needed, and the cost of a medium-voltage (or high-voltage) acquisition device is saved; moreover, a connecting wire of the voltage sensor is not required to be arranged, so that the complexity of the system connecting wire is reduced; furthermore, the arrangement of sampling and communication connecting lines in the system is reduced, and faults caused by damage of the connecting lines are reduced, so that the reliability of the system is improved.
Referring to fig. 4, a flowchart of another photovoltaic grid-connected control method according to an embodiment of the present application is shown, where the method is applied to a control unit or an inverter unit of the system shown in fig. 2, and as shown in fig. 4, the method may include:
and S210, controlling the third switch to be closed, acquiring the voltage of the low-voltage side of the fourth step-up transformer, and calculating to obtain the preset voltage of the low-voltage side of the third step-up transformer according to the voltage of the low-voltage side.
Controlling K5 to be closed, wherein the voltage of the high-voltage side of the fourth step-up transformer is equal to the voltage of the power grid, and then, the amplitude and the phase of the voltage of the low-voltage side of the fourth step-up transformer can be acquired by using a low-voltage sensor and transmitted to the control unit; then, the control unit calculates the amplitude and the phase of the power grid voltage according to the transformation ratio and the phase difference of the fourth step-up transformer; and finally, calculating the amplitude and the phase of the low-voltage side voltage of the third step-up transformer when the third step-up transformer outputs the voltage which is the same as the amplitude and the phase of the power grid voltage according to the calculated amplitude and the phase of the power grid voltage and the transformation ratio and the phase difference of the third step-up transformer, namely the preset voltage.
And S220, controlling at least one inverter switch to be closed, and pre-exciting the third step-up transformer to enable the voltage of the low-voltage side of the third step-up transformer to reach a preset voltage.
The inverter switch may be controlled by an inverter unit. And pre-exciting the third boosting transformer by at least one inversion unit, and detecting whether the voltage at the low-voltage side of the third boosting transformer reaches a preset voltage.
The low-voltage side voltage of the third step-up transformer is the alternating voltage output by the inversion unit connected with the closed inversion switch.
And S230, controlling the main switch to be closed after the voltage of the low-voltage side of the third step-up transformer reaches a preset voltage.
And when the voltage of the low-voltage side of the third booster transformer is detected to reach the preset voltage, the main switch is controlled to be closed, and all the inversion switches are controlled to be closed to complete grid connection of the inversion units.
According to the photovoltaic grid-connected control method provided by the embodiment, the amplitude and the phase of the voltage of the power grid are obtained by collecting the amplitude and the phase of the voltage of the low-voltage side of the fourth step-up transformer. And determining preset voltage required to be reached by the low-voltage side of the third step-up transformer according to the amplitude and the phase of the power grid voltage, pre-exciting the third step-up transformer by at least one inversion unit by using the energy of the direct-current power supply, and closing the main switch to complete grid connection when the low-voltage side voltage of the third step-up transformer reaches the preset voltage. According to the method, the fourth step-up transformer is used for collecting the voltage of the power grid, a high-voltage collecting device with high cost is not needed, and a connecting wire of a voltage sensor is not needed, so that the complexity of the connecting wire of the system is reduced. Furthermore, the arrangement of sampling and communication connecting lines in the system is reduced, and faults caused by damage of the connecting lines are reduced, so that the reliability of the system is improved.
Corresponding to the embodiment of the photovoltaic grid-connected control method shown in fig. 3, the application also provides an embodiment of a photovoltaic grid-connected control device.
Referring to fig. 5, a block diagram of a photovoltaic grid-connected control device according to an embodiment of the present application is shown, where the device is applied to the photovoltaic grid-connected system shown in fig. 1. As shown in fig. 5, the apparatus may include: a first control module 110 and a second control module 120.
And the first control module 110 is configured to control the second switch and the first switch to be closed before grid connection, so that the second step-up transformer performs pre-excitation on the first step-up transformer.
And the second control module 120 is configured to control the main switch to be turned on, control the first switch and the second switch to be turned off, and control the inverter switch to be turned on after detecting the voltage on the low-voltage side of the first step-up transformer.
According to the photovoltaic grid-connected control device provided by the embodiment, the second boosting transformer is used for pre-exciting the first boosting transformer, a medium-voltage (or high-voltage) voltage sensor is not needed, and the cost of a medium-voltage (or high-voltage) acquisition device is saved; moreover, a connecting wire of the voltage sensor is not required to be arranged, so that the complexity of the system connecting wire is reduced; furthermore, the arrangement of sampling and communication connecting lines in the system is reduced, and faults caused by damage of the connecting lines are reduced, so that the reliability of the system is improved.
Corresponding to the embodiment of the photovoltaic grid-connected control method shown in fig. 4, the application also provides a corresponding device embodiment.
Referring to fig. 6, a block diagram of another pv grid-connected control apparatus according to an embodiment of the present disclosure is shown, where the apparatus is applied to the pv grid-connected system shown in fig. 2, and as shown in fig. 6, the apparatus may include: a first control module 210, an acquisition module 220, a calculation module 230, a second control module 240, and a third control module 250.
And the first control module 210 is used for controlling the first switch to be closed before grid connection.
And an obtaining module 220, configured to obtain a low-voltage side voltage of the fourth step-up transformer.
The calculating module 230 is configured to calculate a preset voltage of the low-voltage side of the first step-up transformer according to the low-voltage side voltage, the parameters of the third step-up transformer and the fourth step-up transformer.
And a second control module 240, configured to control at least one of the inverter switches to be turned on, so as to perform pre-excitation on the third step-up transformer, so that a low-voltage side voltage of the third step-up transformer reaches the preset voltage.
And a third control module 250, configured to control the main switch to be turned on after the voltage on the low-voltage side of the third step-up transformer reaches a preset voltage.
According to the photovoltaic grid-connected control device provided by the embodiment, the amplitude and the phase of the voltage of the power grid are obtained by collecting the amplitude and the phase of the voltage of the low-voltage side of the fourth step-up transformer. And determining preset voltage required to be reached by the low-voltage side of the third step-up transformer according to the amplitude and the phase of the power grid voltage, pre-exciting the third step-up transformer by at least one inversion unit by using the energy of the direct-current power supply, and closing the main switch to complete grid connection when the low-voltage side voltage of the third step-up transformer reaches the preset voltage. The device utilizes fourth step-up transformer to gather electric wire netting voltage, does not need the high-pressure acquisition device that use cost is expensive, moreover, need not set up voltage sensor's connecting wire, consequently, has reduced the complexity of system's connecting wire. Furthermore, the arrangement of sampling and communication connecting lines in the system is reduced, and faults caused by damage of the connecting lines are reduced, so that the reliability of the system is improved.
While, for purposes of simplicity of explanation, the foregoing method embodiments have been described as a series of acts or combination of acts, it will be appreciated by those skilled in the art that the present invention is not limited by the illustrated ordering of acts, as some steps may occur in other orders or concurrently with other steps in accordance with the invention. Further, those skilled in the art should also appreciate that the embodiments described in the specification are preferred embodiments and that the acts and modules referred to are not necessarily required by the invention.
It should be noted that, in the present specification, the embodiments are all described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments may be referred to each other. For the device-like embodiment, since it is basically similar to the method embodiment, the description is simple, and for the relevant points, reference may be made to the partial description of the method embodiment.
The steps in the method of the embodiments of the present application may be sequentially adjusted, combined, and deleted according to actual needs.
The device and the modules and sub-modules in the terminal in the embodiments of the present application can be combined, divided and deleted according to actual needs.
In the several embodiments provided in the present application, it should be understood that the disclosed terminal, apparatus and method may be implemented in other manners. For example, the above-described terminal embodiments are merely illustrative, and for example, the division of a module or a sub-module is only one logical division, and there may be other divisions when the terminal is actually implemented, for example, a plurality of sub-modules or modules may be combined or integrated into another module, or some features may be omitted or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or modules, and may be in an electrical, mechanical or other form.
The modules or sub-modules described as separate parts may or may not be physically separate, and parts that are modules or sub-modules may or may not be physical modules or sub-modules, may be located in one place, or may be distributed over a plurality of network modules or sub-modules. Some or all of the modules or sub-modules can be selected according to actual needs to achieve the purpose of the solution of the present embodiment.
In addition, each functional module or sub-module in the embodiments of the present application may be integrated into one processing module, or each module or sub-module may exist alone physically, or two or more modules or sub-modules may be integrated into one module. The integrated modules or sub-modules may be implemented in the form of hardware, or may be implemented in the form of software functional modules or sub-modules.
Finally, it should also be 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.
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.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A grid-connected photovoltaic system, comprising: the device comprises an inversion unit, an inversion switch, a first boosting transformer, a main switch, a second boosting transformer, a first switch, a second switch and a control unit, wherein the phase difference and the transformation ratio of the second boosting transformer and the first boosting transformer are the same, and the second boosting transformer pre-excites the first boosting transformer;
the direct current end of the inversion unit is connected with a direct current power supply, and the alternating current end of the inversion unit is connected with the low-voltage side of the first boosting transformer through the inversion switch;
the high-voltage side of the first booster transformer is connected with one end of the main switch, and the other end of the main switch is connected with a power grid;
one end of the first switch is connected with the low-voltage side of the first boosting transformer, and the other end of the first switch is connected with the low-voltage side of the second boosting transformer;
one end of the second switch is connected with the high-voltage side of the second booster transformer, and the other end of the second switch is connected with the power grid;
the control unit is used for controlling the first switch and the second switch to be closed before grid connection, and controlling the main switch to be closed and controlling the first switch and the second switch to be opened when the low-voltage side voltage of the first boosting transformer is detected.
2. The system according to claim 1, wherein the number of the inversion units and the inversion switches is N, and N is an integer greater than 1;
the direct current end of each inversion unit is connected with a direct current power supply, the alternating current end of each inversion unit is connected with one end of one inversion switch, and the other end of each inversion switch is connected with the low-voltage side of the first boosting transformer after being connected in parallel.
3. The system of claim 1 or 2, wherein the inverter switch, the first switch and the second switch are any one of a combination of a circuit breaker and a load switch plus a fuse.
4. A grid-connected photovoltaic system, comprising: the system comprises an inversion unit, an inversion switch, a third boosting transformer, a main switch, a fourth boosting transformer, a first switch and a control unit;
the direct current end of the inverter unit is connected with a direct current power supply, and the alternating current end of the inverter unit is connected with the low-voltage side of the third boosting transformer through the inverter switch;
the high-voltage side of the third booster transformer is connected with one end of the main switch, and the other end of the main switch is connected with a power grid;
one end of the first switch is connected with the high-voltage side of the fourth step-up transformer, and the other end of the first switch is connected with the power grid;
the control unit is used for controlling the first switch to be closed before grid connection, acquiring the voltage of the low-voltage side of the fourth boosting transformer, and calculating according to the voltage of the low-voltage side, the voltage of the third boosting transformer and the parameter of the fourth boosting transformer to obtain the preset voltage of the low-voltage side of the third boosting transformer;
and the inversion unit is used for pre-exciting the third boosting transformer until the voltage of the low-voltage side of the third boosting transformer reaches the preset voltage, and directly or indirectly controlling the main switch to be switched on.
5. The system according to claim 4, wherein the number of the inversion units and the inversion switches is N, and N is an integer greater than 1;
and the direct current end of each inversion unit is respectively connected with a direct current power supply, the alternating current end of each inversion unit is respectively connected with one end of one inversion switch, and the other end of each inversion switch is connected in parallel and then connected with the low-voltage side of the third step-up transformer.
6. The system of claim 4 or 5, wherein the inverter switch, the first switch and the second switch are any one of a circuit breaker and a load switch plus a fuse.
7. A photovoltaic grid-connected control method is applied to the photovoltaic grid-connected system of any one of claims 1 to 3, and the method comprises the following steps:
before grid connection, the second switch and the first switch are controlled to be closed, so that the second boosting transformer performs pre-excitation on the first boosting transformer;
and when the voltage of the low-voltage side of the first boosting transformer is detected, controlling the main switch to be closed, controlling the first switch and the second switch to be disconnected, and controlling the inversion switch to be closed.
8. A photovoltaic grid-connected control method is applied to the photovoltaic grid-connected system of any one of claims 4 to 6, and the method comprises the following steps:
before grid connection, the first switch is controlled to be closed, and the voltage of the low-voltage side of the fourth boosting transformer is obtained;
calculating to obtain a preset voltage of the low-voltage side of the third step-up transformer according to the low-voltage side voltage, the parameters of the third step-up transformer and the parameters of the fourth step-up transformer;
controlling at least one inverter switch to be switched on, and pre-exciting the third step-up transformer to enable the low-voltage side voltage of the third step-up transformer to reach the preset voltage;
and when the voltage of the low-voltage side of the third step-up transformer reaches a preset voltage, controlling the main switch to be closed.
9. A photovoltaic grid-connected control device applied to the photovoltaic grid-connected system according to any one of claims 1 to 3, the device comprising:
the first control module is used for controlling the second switch and the first switch to be closed before grid connection so as to enable the second boosting transformer to be pre-excited for the first boosting transformer;
and the second control module is used for controlling the main switch to be closed, controlling the first switch and the second switch to be disconnected and controlling the inversion switch to be closed after the voltage of the low-voltage side of the first boosting transformer is detected.
10. A photovoltaic grid-connected control device applied to the photovoltaic grid-connected system according to any one of claims 4 to 6, the device comprising:
the first control module is used for controlling the first switch to be closed before grid connection;
the acquisition module is used for acquiring the low-voltage side voltage of the fourth boosting transformer;
the calculation module is used for calculating and obtaining the preset voltage of the low-voltage side of the third boosting transformer according to the low-voltage side voltage, the parameters of the third boosting transformer and the parameters of the fourth boosting transformer;
the second control module is used for controlling at least one inverter switch to be switched on and pre-exciting the third boosting transformer so as to enable the voltage of the low-voltage side of the third boosting transformer to reach the preset voltage;
and the third control module is used for controlling the main switch to be closed after the voltage of the low-voltage side of the third boosting transformer reaches a preset voltage.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201811109868.XA CN110943472A (en) | 2018-09-21 | 2018-09-21 | Photovoltaic grid-connected system, control method and device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201811109868.XA CN110943472A (en) | 2018-09-21 | 2018-09-21 | Photovoltaic grid-connected system, control method and device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN110943472A true CN110943472A (en) | 2020-03-31 |
Family
ID=69904607
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201811109868.XA Pending CN110943472A (en) | 2018-09-21 | 2018-09-21 | Photovoltaic grid-connected system, control method and device |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN110943472A (en) |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN203415994U (en) * | 2013-07-30 | 2014-01-29 | 阳光电源股份有限公司 | Photovoltaic grid connected inversion system and photovoltaic power generation system equipped therewith |
| CN104242353A (en) * | 2014-10-17 | 2014-12-24 | 阳光电源股份有限公司 | Photovoltaic grid-connected system as well as start control method and start control device |
| JP2015089213A (en) * | 2013-10-30 | 2015-05-07 | 東芝三菱電機産業システム株式会社 | Synchronizing device |
-
2018
- 2018-09-21 CN CN201811109868.XA patent/CN110943472A/en active Pending
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN203415994U (en) * | 2013-07-30 | 2014-01-29 | 阳光电源股份有限公司 | Photovoltaic grid connected inversion system and photovoltaic power generation system equipped therewith |
| JP2015089213A (en) * | 2013-10-30 | 2015-05-07 | 東芝三菱電機産業システム株式会社 | Synchronizing device |
| CN104242353A (en) * | 2014-10-17 | 2014-12-24 | 阳光电源股份有限公司 | Photovoltaic grid-connected system as well as start control method and start control device |
Non-Patent Citations (1)
| Title |
|---|
| 张虹等: "变压器预励磁研究", 《变压器》 * |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US10734944B2 (en) | Inverter having grid disconnection point and insulation resistance measurement and method for measuring an insulation resistance | |
| CN103048544B (en) | Insulation resistance monitoring method of photovoltaic power generation system | |
| CN105337519A (en) | Self-checking system and self-checking method for cascaded multilevel converter | |
| US11616361B2 (en) | Routing power in a power system | |
| WO2011153427A3 (en) | Detection of welded switch contacts in a line converter system | |
| CN108832893A (en) | Photovoltaic module cutoff device, shutdown control method and intelligent assembly | |
| CN109802441A (en) | The direct current arc fault detection method of photovoltaic inverting system, apparatus and system | |
| CN105021977A (en) | AC relay detection method and system before grid connection of photovoltaic inverter | |
| CN111610411A (en) | Cable insulation impedance detection method and device | |
| CN110346708B (en) | Relay fault detection method for photovoltaic grid-connected and off-grid inverter | |
| CN106253332A (en) | A kind of photovoltaic DC-to-AC converter starts method, device and the photovoltaic DC-to-AC converter controlled | |
| ZA202102427B (en) | An electrical protection system and a method thereof | |
| CN110943472A (en) | Photovoltaic grid-connected system, control method and device | |
| CN110311581B (en) | Inverter circuit control method and device and inverter | |
| CN110018384B (en) | Method for detecting a ground fault condition in a power conversion device | |
| CN115494384A (en) | Detection method and circuit for energy storage grid-connected PCS inverter side relay | |
| CN113176468B (en) | Inverter detection method and application device thereof | |
| CN112771749B (en) | Method for testing a separation point of a photovoltaic inverter and photovoltaic inverter of this type | |
| CN115166508B (en) | Failure detection method and relay failure detection device for grid-connected inverter | |
| CN104901212B (en) | The pre-assembled substation room of step-down combining | |
| CN104811027A (en) | Inverter starting method, inverter starting device and inverter starting system | |
| Anjaiah et al. | Real-Time Fault Diagnosis in Photovoltaic Based DC Microgrids Using Modified Change Detection Filter | |
| US11742637B2 (en) | Split bus electrical panel for microgrid applications | |
| CN112217411B (en) | Reactive power converter and soft start and overhaul method thereof | |
| CN106451720A (en) | Super capacitor charging system of self-dumping truck |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| RJ01 | Rejection of invention patent application after publication | ||
| RJ01 | Rejection of invention patent application after publication |
Application publication date: 20200331 |