Grid-connected system, control method, storage medium, and program product

Abstract

The application provides a grid-connected system, a control method, a computer readable storage medium and a computer program product. The grid-connected system comprises: an inverter; a first transformer, a low-voltage side of the first transformer being connected with an alternating-current side of the inverter; a switching device, an input end of the switching device being connected with a high-voltage side of the first transformer, and an output end of the switching device being used for being connected with a power grid; and a first controller, a power supply end of the first controller taking power from the output end of the switching device, and the first controller being used for performing the following operations: determining a voltage of the output end of the switching device according to a power supply voltage of the power supply end; controlling an output voltage of the inverter according to the voltage of the output end of the switching device, so that the voltage of the input end of the switching device and the voltage of the output end of the switching device satisfy a grid-connected condition; and in response to the grid-connected condition being satisfied, controlling the switching device to be closed, so as to transmit alternating current output by the inverter to the power grid.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and more specifically, to a grid-connected system, a control method, a computer-readable storage medium, and a computer program product. Background Technology

[0002] Many grid-connected systems utilize intelligent control units to disconnect switching devices from the grid during no-load operation to reduce transformer no-load losses, and then close the circuit for grid-connected power generation when needed. How to achieve shock-free closing of grid-connected systems is a problem that needs to be solved. Summary of the Invention

[0003] This application provides a grid-connected system, control method, storage medium, and program product that can reduce control costs.

[0004] In a first aspect, a grid-connected system is provided, comprising: an inverter; a first transformer, the low-voltage side of which is connected to the AC side of the inverter; a switching device, the input terminal of which is connected to the high-voltage side of the first transformer, and the output terminal of which is connected to the power grid; and a first controller, the power supply terminal of which draws power from the output terminal of the switching device, and the first controller is configured to perform the following operations: determine the voltage of the output terminal of the switching device based on the supply voltage of the power supply terminal; control the output voltage of the inverter based on the voltage of the output terminal of the switching device, such that the voltage of the input terminal of the switching device and the voltage of the output terminal of the switching device satisfy the grid connection conditions; and, in response to the grid connection conditions being satisfied, control the switching device to close, so as to transmit the AC power output by the inverter to the power grid.

[0005] Optionally, controlling the inverter's output voltage based on the voltage at the output terminal of the switching device includes: determining a target value for the inverter's output voltage based on the voltage at the output terminal of the switching device and the turns ratio of the first transformer; and controlling the inverter's output voltage based on the difference between the target value and the actual value of the inverter's output voltage.

[0006] Optionally, controlling the inverter's output voltage based on the output voltage of the switching device includes: determining the input voltage of the switching device based on the inverter's output voltage and the turns ratio of the first transformer; and controlling the inverter's output voltage based on the difference between the input voltage and the output voltage of the switching device.

[0007] Optionally, the grid-connected system also includes a second controller. One end of the first controller is connected to the inverter, and the other end of the first controller is connected to the second controller. The first controller communicates directly with the inverter to control the output voltage of the inverter. The first controller controls the switching devices to turn on and off through the second controller.

[0008] Optionally, the grid-connected system may also include: a second transformer, the input of which is connected to the output of the switching device, and the output of which is connected to the power supply of the first controller.

[0009] Secondly, a control method is provided for a grid-connected system, the grid-connected system comprising: an inverter; a first transformer, the low-voltage side of the first transformer being connected to the AC side of the inverter; a switching device, the input terminal of the switching device being connected to the high-voltage side of the first transformer, and the output terminal of the switching device being connected to the power grid; and a first controller, the power supply terminal of the first controller drawing power from the output terminal of the switching device. The control method comprises: determining the voltage of the output terminal of the switching device based on the supply voltage of the power supply terminal; controlling the output voltage of the inverter based on the voltage of the output terminal of the switching device, such that the voltage of the input terminal and the voltage of the output terminal of the switching device satisfy the grid connection conditions; and, in response to the grid connection conditions being satisfied, controlling the switching device to close, so as to transmit the AC power output by the inverter to the power grid.

[0010] Optionally, controlling the inverter's output voltage based on the voltage at the output terminal of the switching device includes: determining a target value for the inverter's output voltage based on the voltage at the output terminal of the switching device and the turns ratio of the first transformer; and controlling the inverter's output voltage based on the difference between the target value and the actual value of the inverter's output voltage.

[0011] Optionally, controlling the inverter's output voltage based on the output voltage of the switching device includes: determining the input voltage of the switching device based on the inverter's output voltage and the turns ratio of the first transformer; and controlling the inverter's output voltage based on the difference between the input voltage and the output voltage of the switching device.

[0012] Thirdly, a control device is provided, characterized in that it includes a processor and a memory, the memory being used to store programs, instructions or code, and the processor being used to execute the programs, instructions or code in the memory to perform the methods described above.

[0013] Fourthly, a computer-readable storage medium is provided, characterized in that it stores program code thereon, the program code being used to control a grid-connected system to perform the method as described above.

[0014] To achieve shockless closing of grid-connected systems, related technologies typically use voltage sampling devices to obtain the output voltage of switching devices for controlling their opening and closing. However, the use of voltage sampling devices increases control costs. Unlike related technologies, the embodiments of this application calculate the output voltage of the switching devices based on the supply voltage from their output terminals, thus eliminating the need for voltage sampling devices. This achieves both shockless closing of grid-connected systems and reduces control costs. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a structural example diagram of a grid-connected system in related technologies.

[0017] Figure 2 This is a structural example diagram of the grid-connected system provided in the embodiments of this application.

[0018] Figure 3 This is a flowchart illustrating the control method provided in an embodiment of this application.

[0019] Figure 4 This is an example diagram of the triangular phase relationship provided in the embodiments of this application.

[0020] Figure 5 yes Figure 3 A flowchart illustrating the operation of the control method S320.

[0021] Figure 6 yes Figure 3 Another flowchart illustrating the operation of the control method S320.

[0022] Figure 7 This is a circuit example diagram of the grid-connected system provided in the embodiments of this application.

[0023] Figure 8 A schematic diagram of the control device provided in the embodiments of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained based on the embodiments of this application are within the scope of protection of this application.

[0025] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0026] It should be understood that the embodiments described below are merely for explaining this application and are not intended to limit this application.

[0027] In some grid-connected systems, various forms of energy, such as solar, hydro, and chemical energy, are typically converted into direct current (DC) through energy conversion units. For example, in a photovoltaic (PV) grid-connected system, solar energy is converted into DC by photovoltaic modules. Then, the DC is converted into alternating current (AC) by an inverter, and the AC is stepped up by a transformer before being supplied to the grid. For instance, the AC is stepped up by a transformer in a medium-voltage transformer substation before being supplied to the grid. Because the power output of the grid is significantly reduced at certain times, such as at night, the transformer may operate under no-load conditions. No-load operation leads to unnecessary transformer losses. Therefore, many grid-connected systems employ intelligent switching technology. For example... Figure 1 As shown, this technology involves connecting a switching device 103 in series on the collector line of transformer 102. The controller of the switching device 103 is called an intelligent control unit 107. The intelligent control unit 107 is used to control the switching device 103 to disconnect from the grid during no-load operation in order to reduce no-load losses, and to close the switch for grid-connected power generation when needed.

[0028] In related technologies, to achieve impact-free closing, the intelligent control unit 107 samples the voltage across the switching device 103 using two voltage sampling devices 105 and 106, such as... Figure 1 As shown. The voltage at the end of the switching device 103 closest to the transformer 102 is usually called the input voltage, while the voltage at the end closest to the power grid is usually called the output voltage. The intelligent control unit 107 determines whether the conditions for shockless closing are met by comparing the sampled input and output voltages of the transformer 102. The conditions for shockless closing, also known as grid connection conditions, refer to conditions that ensure the closing of the switching device will not cause an impact on the power grid. If the output and input voltages of the transformer 102 do not meet the grid connection conditions, for example, if the difference between them is large, the intelligent control unit 107 controls the output voltage of the inverter 101 through the intelligent unit 104 (i.e., the inverter controller), so that the output voltage of the transformer 102 changes in accordance with the output voltage of the inverter 101. Until the output and input voltages of the transformer 102 meet the grid connection conditions, for example, when the difference between the sampled output and input voltages of the transformer 102 is within the allowable range, the intelligent control unit 107 controls the switching device to close, thereby achieving shockless closing.

[0029] It can be seen that the above-mentioned switching control method requires the addition of voltage sampling devices 105 and 106, which increases the control cost.

[0030] This application provides a grid-connected system that can reduce or avoid the use of voltage sampling equipment for intelligent control of switching devices, thereby reducing costs.

[0031] like Figure 2 As shown in the figure, an embodiment of this application provides a grid-connected system 20, including an inverter 201 and a first transformer 202. The low-voltage side of the first transformer 202 is connected to the AC side of the inverter 201.

[0032] The inverter 201 is used to convert the obtained direct current (DC) into alternating current (AC). For example, the DC side of the inverter 201 can be connected to a photovoltaic (PV) module, which converts solar energy into DC, and the inverter 201 converts the DC into AC. The DC side of the inverter 201 can be connected to various energy conversion components, not limited to PV modules, such as energy storage devices.

[0033] The first transformer 202 is used to step up the AC power and supply it to the power grid. The turns ratio of the first transformer 202 can be a fixed value or a configurable value. The first transformer can be located, for example, in a medium-voltage transformer substation.

[0034] like Figure 2 As shown, the grid-connected system 20 also includes a switching device 203. The input terminal of the switching device 203 is connected to the high-voltage side of the first transformer 202. The output terminal of the switching device 203 is used to connect to the grid side. In some scenarios, the switching device 203 is also referred to as a medium-voltage switch.

[0035] like Figure 2 As shown, the grid-connected system 20 also includes a first controller 205. The power supply terminal of the first controller 205 draws power from the output terminal of the switching device 203.

[0036] In some embodiments, a second transformer 204 can be connected between the output terminal of the switching device 203 and the power supply terminal of the first controller 205. The input terminal of the second transformer 204 is connected to the output terminal of the switching device 203, and the output terminal of the second transformer 204 is connected to the power supply terminal of the first controller 205. The second transformer 204 is used to step down the voltage at the output terminal of the switching device 203 to supply power to the first controller 205. In some embodiments, the second transformer 204 can be connected to any one phase of the three-phase voltage output by the switching device 203.

[0037] It should be noted that connecting the second transformer 204 to the output terminal of the switching device 203 is only an example. Power can also be drawn from the output terminal of the switching device 203 to power the first controller 205 in other ways.

[0038] The first controller 205 is used to execute the control method. For example... Figure 3As shown, the control method may include the following operations S310 to S330.

[0039] In operation S310, the first controller 205 determines the voltage at the output terminal of the switching device 203 based on the supply voltage at its power supply terminal.

[0040] Taking the connection of a second transformer 204 to the output terminal of the switching device 203 as an example, the second transformer 204 steps down the voltage at the output terminal of the switching device 203 to supply power to the first controller 205. Therefore, the first controller 205 can calculate the voltage at the output terminal of the switching device 203 based on the supply voltage at the power supply terminal and the turns ratio of the second transformer 204. The voltage referred to in this document includes the voltage amplitude and / or phase value.

[0041] For example, assuming the second transformer 204 is connected to phases AB of the output voltage of the switching device 203, the turns ratio of the second transformer 204 is k1, and the phase of the supply voltage at the power supply terminal of the first controller 205 is θ1, and the amplitude is U1, then the first controller 205 can calculate the phase θ of the three-phase voltage at the output terminal of the switching device 203 based on the phase triangle relationship. 1ab θ 1bc θ 1ca With amplitude U 1ab U 1bc U 1ca For example, the phase triangle relationship is as follows: Figure 4 As shown, the formulas for calculating the phase and amplitude of the three-phase voltage at the output of the switching device 203 can be:

[0042] θ 1ab =θ1, θ 1bc =θ1–120°, θ 1ca =θ1 + 120°;

[0043] U 1ab =U 1bc =U 1ca =k1*U1.

[0044] In operation S320, the first controller 205 controls the output voltage of the inverter 201 according to the voltage at the output terminal of the switching device 203, so that the voltage at the input terminal of the switching device 203 and the voltage at the output terminal of the switching device 203 meet the grid connection conditions.

[0045] See Figure 2The output voltage of inverter 201 is boosted by the first transformer 202 and then input to switching device 203. Therefore, the voltage at the input terminal of switching device 203 changes in accordance with the output voltage of inverter 201. Thus, the first controller 205 can control the input voltage of switching device 203 by controlling the output voltage of inverter 201, ensuring that the input and output voltages of switching device 203 meet grid connection requirements. The first controller 205 can achieve the above control in various ways, which will be described in detail later.

[0046] Setting grid connection conditions is to prevent significant impacts on the grid voltage after the switch is closed. For example, if the voltage amplitude at the input terminal of switch 203 is much greater or less than the output voltage when switch 203 is closed, the output voltage of switch 203 will change drastically after closing. Since the output voltage of switch 203 is connected to the grid side, this drastic change in output voltage will impact the grid voltage. Another example is if the phase difference between the input and output voltages of switch 203 is large when switch 203 is closed, the phase difference will generate a large inrush current, causing grid voltage fluctuations and potentially damaging equipment such as transformers. Therefore, grid connection conditions need to be set to avoid these effects. For example, the grid connection condition could be that the input voltage of switch 203 matches the output voltage of switch 203. In some scenarios, the grid connection condition could be that the input and output voltages of switch 203 meet predetermined conditions. Alternatively, the grid connection condition can be that the difference between the voltage at the input terminal and the voltage at the output terminal of the switching device 203 meets a predetermined condition. Alternatively, the grid connection condition can be that the amplitude difference and phase difference of each phase of the voltage at the input terminal and the voltage at the output terminal of the switching device 203 are both within their respective allowable ranges. Alternatively, the grid connection condition can be that the amplitude difference and phase difference of each phase of the voltage at the input terminal and the voltage at the output terminal of the switching device 203 are less than a threshold value. In this way, controlling the closing of the switching device 203 when the grid connection condition is met can avoid impact on the power grid and damage to equipment.

[0047] In operation S330, in response to the grid connection conditions being met, the first controller 205 controls the switching device 203 to close, so as to transmit the AC power output by the inverter 201 to the power grid.

[0048] As described above, when the grid connection conditions are met, closing the switching device 203 will not cause a significant impact on the power grid. At this time, the first controller 205 can control the switching device 203 to close so as to transmit the AC power output by the inverter 201 to the power grid.

[0049] In the above embodiments, the power supply terminal of the first controller 205 draws power from the output terminal of the switching device 203, and the first controller 205 calculates the voltage of the output terminal of the switching device 203 based on the power supply voltage of its power supply terminal. Compared with the related art, which obtains the voltage of the output terminal of the switching device 203 through a voltage sampling device, the embodiments of this application can reduce the voltage sampling device, thereby reducing costs.

[0050] In operation S320, the first controller 205 can control the output voltage of the inverter 201 based on the output voltage of the switching device 203 in various ways, so that the input and output voltages of the switching device 203 meet the grid connection conditions. The following examples illustrate this in detail.

[0051] In one exemplary implementation of the operation of S320, the switching device, such as Figure 5 As shown, operation S320 may include operations S322A and S324A.

[0052] In operation S322A, the first controller 205 determines the voltage at the input terminal of the switching device 203 based on the output voltage of the inverter 201 and the turns ratio of the first transformer 202.

[0053] A communication link may exist between the inverter 201 and the first controller 205, through which the inverter can report its output voltage to the first controller 205. This communication link can utilize technologies such as PLC communication, RS-485 communication, Ethernet cable, fiber optic cable, Bluetooth, and Wi-Fi. Alternatively, the first controller 205 can obtain the output voltage of the inverter 201 from its controller (e.g., the intelligent unit 104 in related technologies). Therefore, the first controller 205 can calculate the voltage at the input terminal of the switching device 203 based on the output voltage of the inverter 201 and the turns ratio of the first transformer 202.

[0054] For example, the phase value of the three-phase voltage output by inverter 201 is θ 2ab θ 2bc θ 2ca The amplitude is U 2ab U 2bc U 2ca If the turns ratio of the first transformer 202 is k2, then the phase θ of the voltage at the input terminal of the switching device 203 is... 1ab '、θ 1bc '、θ 1ca It can be calculated as:

[0055] θ 1ab '=θ 2ab θ 1bc '=θ 2bc θ 1ca'=θ 2ca ;

[0056] The phase U of the voltage at the input terminal of the switching device 203 1ab '、U 1bc '、U 1ca It can be calculated as:

[0057] U 1ab '=k2*U 2ab U 1bc '=k2*U 2bc U 1ca '=k2*U 2ca .

[0058] In operation S324A, the first controller 205 controls the output voltage of the inverter 201 based on the difference between the voltage at the input terminal of the switching device 203 and the voltage at the output terminal of the switching device 203.

[0059] For example, the first controller 205 can calculate the difference between the voltage at the input terminal of the switching device 203 and the voltage at the output terminal of the switching device 203. When the difference is large, a control command is generated to reduce the output voltage of the inverter 201, and the control command is sent to the inverter 201. For example, the first controller 205 can forward the control command to the inverter 201 through the intelligent unit on the medium-voltage transformer side. Alternatively, the function of the first controller 205 can be set in the intelligent unit on the medium-voltage transformer side, so that the control command can be directly sent to the inverter 201.

[0060] As can be seen, according to this embodiment, the first controller 205 calculates the voltage at the input terminal of the switching device 203 based on the output voltage of the inverter 201 reported by the inverter 201 and the turns ratio of the first transformer 202. Therefore, it is not necessary to sample the voltage at the input terminal of the switching device 203, thus eliminating the need for a voltage sampling device at the input terminal of the switching device 203. Therefore, by combining operation S310 and operations S322A and S322B, this embodiment can simultaneously save the voltage sampling device at both ends of the switching device 203, further reducing costs.

[0061] In another exemplary implementation of operating S320, such as Figure 6 As shown, operation S320 may include operations S322B and S324B. The first controller 205 may perform operations S322B and S324B to control the output voltage of the inverter 201 according to the voltage at the output terminal of the switching device 203, so that the voltage at the input terminal and the voltage at the output terminal of the switching device 203 meet the grid connection conditions.

[0062] In operation S322B, the target value of the output voltage of inverter 201 is determined based on the voltage at the output terminal of switching device 203 and the turns ratio of the first transformer 202.

[0063] refer to Figure 2 It is understandable that, in order to meet the grid connection requirements, the first controller 205 can use the calculated voltage value at the output terminal of the switching device 203 as the target value of the input voltage of the switching device 203. Then, the first controller 205 can calculate the target value of the output voltage of the inverter 201 in conjunction with the turns ratio of the first transformer 202.

[0064] For example, the phase of the three-phase voltage at the output of the switching device 203 is θ 1ab θ 1bc θ 1ca The amplitude is U 1ab U 1bc U 1ca If the turns ratio of the first transformer 202 is k2, then the target phase value θ of the three-phase voltage output by the inverter 201 is... 2ab θ 2bc θ 2ca With the target value U 2ab U 2bc U 2ca It can be calculated as follows:

[0065] θ 2ab =θ 1ab θ 2bc =θ 1bc θ 2ca =θ 1ca ;

[0066] U 2ab =U 2bc =U 2ca =U 1ab / k2=U 1bc / k2=U 1ca / k2.

[0067] The turns ratio of the first transformer 202 can be a fixed value and can be directly written into the control logic of the first controller 205. Alternatively, the turns ratio of the first transformer 202 can also be a configurable value. In this case, the first controller 205 can obtain the turns ratio of the first transformer 202 based on the configuration information.

[0068] In operation S324B, the output voltage of inverter 201 is controlled based on the difference between the target value of the output voltage of inverter 201 and the actual value of the output voltage of inverter 201.

[0069] As described above, a communication link can exist between the inverter 201 and the first controller 205. The inverter 201 can report its output voltage, i.e., the actual value of its output voltage, to the first controller 205 through this communication link. Alternatively, the first controller 205 can obtain the actual value of the inverter 201's output voltage from the inverter 201's controller. Therefore, the first controller 205 can calculate the difference between the calculated target value of the inverter 201's output voltage and the obtained actual value. The first controller 205 can generate a control command based on this difference and send it to the inverter 201 to control its output voltage. Alternatively, the first controller 205 can send the difference to the inverter 201, and the inverter 201 can change its output voltage based on the difference. For example, when the actual value of the inverter 201's output voltage is much higher than the target value, the inverter 201 will reduce its output voltage.

[0070] It is understandable that, since the output voltage of inverter 201 has a fixed ratio to the input voltage of switching device 203 (i.e., the turns ratio of the first transformer 202), the difference between the target and actual values ​​of the output voltage of inverter 201 also has a fixed ratio to the difference between the target and actual values ​​of the input voltage of switching device 203. Simultaneously, the target value of the input voltage of switching device 203 is equal to the actual voltage of its output, i.e., the voltage calculated by the first controller 205. Therefore, the difference between the target and actual values ​​of the output voltage of inverter 201 also has a fixed proportional relationship to the difference between the actual values ​​of the input and output of switching device 203. Therefore, controlling the difference between the target and actual values ​​of the output voltage of inverter 201 is equivalent to controlling the difference between the actual values ​​of the input and output of switching device 203. Therefore, the difference between the target and actual values ​​of the output voltage of inverter 201 can be controlled to meet the grid connection conditions. In this embodiment, the grid connection condition can be that the voltage amplitude difference and phase difference of the three-phase voltage output by the inverter 201 are both within the allowable error range.

[0071] Through operations S322B and S324B, the first controller 205 controls the difference between the target value and the actual value of the output voltage of the inverter 201 to ensure that the difference between the actual value at the input terminal and the actual value at the output terminal of the switching device 203 meets the grid connection conditions. Therefore, it is not necessary to sample the voltage at the input terminal of the switching device 203, i.e., no voltage sampling device is required at the input terminal of the switching device 203. Thus, by combining operations S310 and S322B and S324B, this embodiment can simultaneously save on voltage sampling devices at both ends of the switching device 203, further reducing costs.

[0072] It can be seen that by operating either of the two exemplary implementations of S320, the voltage sampling device at the input terminal of the switching device 203 can be saved by indirectly calculating the voltage at the input terminal of the switching device 203. This further reduces costs based on saving the voltage sampling device at the output terminal of the switching device 203 by operating S310. However, it should be noted that in this embodiment, operation S320 is not limited to the two exemplary implementations described above. For example, the first controller 205 can also obtain the voltage at the input terminal of the switching device 203 through a voltage sampling unit at the input terminal of the switching device 203, and determine whether the grid connection conditions are met based on the sampled voltage at the input terminal of the switching device 203 and the calculated voltage at the output terminal of the switching device 203. Compared with the solutions provided by related technologies, the above solutions retain the voltage sampling unit at the input terminal of the switching device 203 but eliminate the voltage sampling unit at the output terminal of the switching device 203, which can also reduce system costs to a certain extent.

[0073] In the above embodiments, the first controller 205 can be a standalone controller. To reduce costs and the complexity of the control link, the functionality of the first controller 205 can be integrated into the controller of the switching device 203. Alternatively, the first controller 205 can be the controller of the switching device 203. The controller of the switching device 203 refers to a controller that has a control link with the switching device and can directly control the closing or opening of the switching device 203 through this control link, such as the intelligent control unit 107 in related technologies.

[0074] When the first controller 205 is the controller of the switching device 203, the first controller 205 can directly control the switching device 203 to close or open. However, in this case, when the first controller 205 controls the output of the inverter 201, it needs to first send the control command to the controller of the inverter 201, such as the intelligent unit 104 in related technologies, and then the intelligent unit 104 forwards it to the inverter 201 for control. This method results in a long communication link and a large communication delay. Therefore, when the grid voltage fluctuates, it may even lead to situations where the circuit cannot be closed or the closing impact is too large due to the control delay.

[0075] For the reasons mentioned above, in some embodiments, the first controller 205 can be a controller that communicates directly with the inverter 201 (which may correspond to the intelligent unit 104 in the related art). The first controller 205 can be located on one side of the first transformer 202. Since the first transformer is usually located in a transformer substation, the first controller 205 can also be called the substation-side controller. In this case, the first controller 205 can communicate directly with the inverter 201 to control the output voltage of the inverter 201, thereby shortening the communication link and reducing communication latency. When the grid connection conditions are met, the first controller 205 can send a closing instruction to the switching device 203 through the second controller (not shown in the figure, the second controller refers to the controller of the switching device 203) to control the switching device 203 to close. This application does not specifically limit the communication method between the first controller 205 and the inverter 201, or the communication method between the first controller and the second controller. For example, communication can be conducted using PLC communication, RS-485 communication, network cable, fiber optic, Bluetooth, WIFI, etc.

[0076] It should be noted that the "connection" mentioned in the above embodiments can refer to either a wired connection or a wireless connection.

[0077] Any of the above embodiments and examples and their technical features can be combined arbitrarily and are within the protection scope of this application.

[0078] To help those skilled in the art better understand the technical solution of this application, a specific example is provided below.

[0079] like Figure 7As shown, multiple inverters 7011, ..., 701n are connected to their respective first transformers 7021, ..., 702n. In practical applications, each inverter 7011, ..., 701n can be a string of multiple inverters. The multiple inverters 7011, ..., 701n also have communication connections with their respective intelligent units 7051, ..., 705n. The intelligent units 7051, ..., 705n can control the inverters 7011, ..., 701n respectively. The first transformers 7021, ..., 702n are used to boost the AC power generated by the corresponding inverters 7011, ..., 701n and converge it onto the hub circuit. A switching device 703 is connected in series in the hub circuit. A second transformer 704 is connected to phases AB of the voltage at the output of the switching device 703. The second transformer 704 steps down the voltage to power the switching device 703, the intelligent control unit 707 of the switching device 703, and each intelligent unit 7051, ..., 705n.

[0080] The functions of the first controller are deployed in each intelligent unit 7051, ..., 705n. Specifically, each intelligent unit 7051, ..., 705n executes steps 1 to 7, which will be explained below using intelligent unit 7051 as an example. It can be understood that the steps executed by each intelligent unit 7051, ..., 705n are similar to those of intelligent unit 7051.

[0081] Step 1: The intelligent unit 7051 determines the phase sequence of power draw from the output terminal of the switching device 703, the voltage transformation k1 of the second transformer 704, and the corresponding turns ratio k2 of the first transformer 7021.

[0082] In this example, since the second transformer 704 is connected to the AB phase of the output voltage of the switching device 703, and the second transformer 704 supplies power to the intelligent unit 7051, the intelligent unit 7051 determines that the phase sequence for drawing power from the output terminal of the switching device 703 is the AB phase.

[0083] k1 and k2 are, for example, both high voltage and low voltage. k1 and k2 can be fixed values. In this case, k1 and k2 can be written into the control logic of the intelligent unit 7051. In some scenarios, k1 and k2 can also be set through a configuration interface, allowing adjustment according to different field conditions. In this case, the intelligent unit 7051 can obtain the values ​​of k1 and k2 from the configuration information.

[0084] Step 2: The intelligent unit 7051 calculates the real-time phase θ1 and amplitude U1 of the power supply voltage based on the sampled power supply voltage data.

[0085] Step 3: The intelligent unit 7051 calculates the phase θ of the three-phase voltage at the output terminal of the switching device 703 based on the real-time phase θ1 and amplitude U1 of the supply voltage, the phase triangle relationship, and the step-down ratio k1. 1ab θ 1bc θ 1ca With amplitude U 1ab U 1bc U 1ca .

[0086] For example, if the intelligent unit 7051 draws power from the AB phase of the output terminal of the switching device 703, then according to... Figure 4 Given the phase triangle relationship shown, the formula for calculating the phase of the three-phase voltage at the output of the switching device 703 can be:

[0087] θ 1ab =θ1, θ 1bc =θ1–120°, θ 1ca =θ1 + 120°;

[0088] The formula for calculating the amplitude of the three-phase voltage at the output terminal of the switching device 703 can be:

[0089] U 1ab =U 1bc =U 1ca =k1*U1.

[0090] Step 4: The intelligent unit 7051 calculates the target phase value θ of the three-phase voltage output by the inverter 7011 based on the phase and amplitude of the three-phase voltage at the output of the switching device 703 and the turns ratio k2 of the first transformer 7021. 2ab θ 2bc θ 2ca With the target value U 2ab U 2bc U 2ca .

[0091] For example, the formula for calculating the target phase value of the three-phase voltage output by inverter 7011 is:

[0092] θ 2ab =θ 1ab θ 2bc =θ 1bc θ 2ca =θ 1ca ;

[0093] The formula for calculating the target amplitude of the three-phase voltage output by inverter 7011 is as follows:

[0094] U 2ab =U 2bc =U 2ca =U 1ab / k2=U 1bc / k2=U 1ca / k2.

[0095] Step 5: The intelligent unit 7051 reads the real-time phase θ of the three-phase voltage output by the inverter 7011 from the inverter 7011 side. 3ab θ 3bc θ 3ca With real-time amplitude U 3ab U 3bc U 3ca .

[0096] Step 6: The intelligent unit 7051 calculates the phase difference Δθ between the target value and the real-time value of the three-phase voltage output by the inverter 7011. ab , Δθ bc , Δθ ca The difference in amplitude ΔU ab ΔU bc ΔU ca It is then sent to inverter 7011 to control the output voltage of inverter 7011.

[0097] For example, the formula for calculating the phase difference mentioned above is:

[0098] Δθ ab =θ 2ab –θ 3ab ;Δθ ab =θ 2bc –θ 3bc ;Δθ ca =θ 2ca –θ 3ca ;

[0099] The formula for calculating the above amplitude difference is:

[0100] ΔU ab =U 2ab –U 3ab ;ΔU ab =U 2bc –U 3bc ;ΔU ca =U 2ca –U 3ca .

[0101] The intelligent unit 7051 can send the aforementioned phase difference and amplitude difference to the inverter 7011 through technologies such as PLC communication, RS-485 communication, network cable, optical fiber, Bluetooth, and WIFI. This application embodiment does not impose any limitations on these technologies.

[0102] Step 7, the voltage amplitude difference ΔU of the three-phase voltage output by inverter 7011. ab ΔU bc ΔUca Phase difference Δθ ab , Δθ bc , Δθ ca When all are within the allowable error range, the intelligent unit 7051 sends a closing command to the intelligent control unit of the switching device 703 to achieve impact-free closing.

[0103] For example, the intelligent unit 7051 can send a closing command to the intelligent control unit of the switching device 703 through technologies such as PLC communication, RS-485 communication, network cable, optical fiber, Bluetooth, and WIFI. This application embodiment does not limit this.

[0104] In the above example, the intelligent unit 7051 calculates the phase and amplitude of the three-phase voltage at the output of the switching device 703 based on the real-time phase and amplitude of the supply voltage, the phase triangle relationship, and the step-down ratio. Therefore, it is not necessary to set up a voltage sampling device at the output of the switching device 703, reducing control costs. Simultaneously, the intelligent unit 7051 also does not need to set up a voltage sampling device at the input of the switching device 703. Instead, based on the phase and amplitude of the three-phase voltage at the output of the switching device 703 and the turns ratio of the first transformer 7021, it calculates the target phase and amplitude values ​​of the three-phase voltage output by the inverter 7011, and controls the output voltage of the inverter 7011 based on the phase difference and amplitude difference between the target value and the real-time value of the three-phase voltage output by the inverter 7011. It is evident that in this embodiment, the characteristics of three-phase AC voltage are fully utilized to obtain the amplitude and phase information of the input and output voltages of the switching device 703 through indirect calculation. Therefore, no voltage sampling device needs to be added at the input and output of the switching device 703, significantly reducing system costs. Furthermore, since the intelligent opening and closing control function is transferred from the intelligent control unit of the switching device 703 to the intelligent unit 7051 of each medium-voltage transformer, the output voltage of the inverter 7011 can be directly obtained through the communication link between the intelligent unit 7051 and the inverter 7011 for calculation and to obtain control commands. Moreover, control commands can be directly sent to the inverter 7011 through the communication link between the intelligent unit 7051 and the inverter 7011, thereby shortening the control link, reducing the delay time, improving the real-time performance of the control, and making the closing stability higher.

[0105] This application also provides a control method applied to a grid-connected system, the grid-connected system including: an inverter; a first transformer, the low-voltage side of the first transformer being connected to the AC side of the inverter; a switching device, the input terminal of the switching device being connected to the high-voltage side of the first transformer, and the output terminal of the switching device being used to connect to the power grid; and a first controller, the power supply terminal of the first controller drawing power from the output terminal of the switching device.

[0106] like Figure 3As shown, the control method may include: determining the output voltage of the switching device based on the supply voltage of the power supply terminal; controlling the output voltage of the inverter based on the output voltage of the switching device, so that the input voltage and the output voltage of the switching device meet the grid connection conditions; and controlling the switching device to close in response to the grid connection conditions being met, so as to transmit the AC power output by the inverter to the power grid.

[0107] One possible implementation is to control the inverter's output voltage based on the voltage at the output terminal of the switching device. This can include: determining a target value for the inverter's output voltage based on the voltage at the output terminal of the switching device and the turns ratio of the first transformer; and controlling the inverter's output voltage based on the difference between the target value and the actual value of the inverter's output voltage.

[0108] As one possible implementation, controlling the inverter's output voltage based on the output voltage of the switching device can include: determining the input voltage of the switching device based on the inverter's output voltage and the turns ratio of the first transformer; and controlling the inverter's output voltage based on the difference between the input voltage and the output voltage of the switching device.

[0109] This application provides a control device including a processor and a memory. The memory is used to store programs, instructions, or code, and the processor is used to execute the programs, instructions, or code in the memory to perform the methods described in the foregoing embodiments.

[0110] In this embodiment, please refer to Figure 8 The control device may include a memory 801 and a processor 802. The processor 802 can be connected to the grid-connected system mentioned above, thereby issuing control commands to the grid-connected system. The memory may be random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (Electronic Programmable ROM), registers, hard disk, removable disk, etc.

[0111] The memory 801 can store computer instructions. When the computer instructions stored in the memory 801 are executed by the processor 802, the processor 802 can be used to execute the control methods described in the preceding embodiments.

[0112] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape) or a semiconductor medium (e.g., solid-state disk (SSD)).

[0113] This application also provides a readable storage medium for storing the methods or algorithms provided in the above embodiments. Examples include random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (Electronic Programmable ROM), registers, hard disks, removable disks, or any other form of storage medium in the art.

[0114] It is understood that the "connection" in the above embodiments should be understood as "electrical connection" or "communication connection" if the connected circuits, modules, units, etc. can transmit electrical signals or data to each other.

[0115] It is understood that the specific examples in this document are only intended to help those skilled in the art better understand the embodiments of this application, and are not intended to limit the scope of the invention.

[0116] It is understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0117] It is understood that the various embodiments described in this application can be implemented individually or in combination, and the embodiments of this application are not limited in this respect.

[0118] Unless otherwise stated, all technical and scientific terms used in the embodiments of this application have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items. The singular forms "a," "the," and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0119] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0120] The above description is merely a specific embodiment of this application, but the scope of protection of this invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this invention should be determined by the scope of the claims.

Claims

1. A grid-connected system, characterized in that, include: Inverter; The first transformer has its low-voltage side connected to the AC side of the inverter. A switching device, wherein the input terminal of the switching device is connected to the high-voltage side of the first transformer, and the output terminal of the switching device is used to connect to the power grid; A first controller, whose power supply terminal draws power from the output terminal of the switching device, and the first controller is configured to perform the following operations: The voltage at the output terminal of the switching device is determined based on the supply voltage at the power supply terminal; The output voltage of the inverter is controlled according to the voltage at the output terminal of the switching device, so that the voltage at the input terminal of the switching device and the voltage at the output terminal of the switching device meet the grid connection conditions. In response to the grid connection conditions being met, the switching device is controlled to close, so as to transmit the AC power output by the inverter to the power grid.

2. The grid-connected system according to claim 1, characterized in that, The step of controlling the output voltage of the inverter based on the voltage at the output terminal of the switching device includes: The target value of the inverter's output voltage is determined based on the voltage at the output terminal of the switching device and the turns ratio of the first transformer. The output voltage of the inverter is controlled based on the difference between the target value of the inverter's output voltage and the actual value of the inverter's output voltage.

3. The grid-connected system according to claim 1, characterized in that, The step of controlling the output voltage of the inverter based on the voltage at the output terminal of the switching device includes: The voltage at the input terminal of the switching device is determined based on the output voltage of the inverter and the turns ratio of the first transformer. The output voltage of the inverter is controlled based on the difference between the voltage at the input terminal of the switching device and the voltage at the output terminal of the switching device.

4. The grid-connected system according to any one of claims 1 to 3, characterized in that, The grid-connected system also includes a second controller. One end of the first controller is connected to the inverter, and the other end of the first controller is connected to the second controller. The first controller communicates directly with the inverter to control the output voltage of the inverter. The first controller controls the switching devices to turn on and off through the second controller.

5. The grid-connected system according to any one of claims 1 to 3, characterized in that, The grid-connected system also includes: The second transformer has its input terminal connected to the output terminal of the switching device, and its output terminal connected to the power supply terminal of the first controller.

6. A control method, characterized in that, The control method is applied to a grid-connected system, the grid-connected system comprising: Inverter; The first transformer has its low-voltage side connected to the AC side of the inverter. A switching device, wherein the input terminal of the switching device is connected to the high-voltage side of the first transformer, and the output terminal of the switching device is used to connect to the power grid; The first controller draws power from the output of the switching device. The control method includes: The voltage at the output terminal of the switching device is determined based on the supply voltage at the power supply terminal; The output voltage of the inverter is controlled according to the voltage at the output terminal of the switching device, so that the voltage at the input terminal of the switching device and the voltage at the output terminal of the switching device meet the grid connection conditions. In response to the grid connection conditions being met, the switching device is controlled to close, so as to transmit the AC power output by the inverter to the power grid.

7. The control method according to claim 6, characterized in that, The step of controlling the output voltage of the inverter based on the voltage at the output terminal of the switching device includes: The target value of the inverter's output voltage is determined based on the voltage at the output terminal of the switching device and the turns ratio of the first transformer. The output voltage of the inverter is controlled based on the difference between the target value of the inverter's output voltage and the actual value of the inverter's output voltage.

8. The control method according to claim 6, characterized in that, The step of controlling the output voltage of the inverter based on the voltage at the output terminal of the switching device includes: The voltage at the input terminal of the switching device is determined based on the output voltage of the inverter and the turns ratio of the first transformer. The output voltage of the inverter is controlled based on the difference between the voltage at the input terminal of the switching device and the voltage at the output terminal of the switching device.

9. A control device, characterized in that, It includes a processor and a memory, the memory being used to store programs, instructions, or code, and the processor being used to execute the programs, instructions, or code in the memory to perform the method as described in any one of claims 6-8.

10. A computer-readable storage medium, characterized in that, The system contains a computer program that is loaded by a processor to perform the method as described in any one of claims 6-8.

Images