Soft start method and device for string-type photovoltaic grid-connected inverter, and storage medium

Abstract

The present invention discloses a soft start method and device for a string-type photovoltaic grid-connected inverter, and a storage medium. The start method includes: disconnecting the grid-connected switch; detecting the open-circuit voltage of each photovoltaic string and sorting them from high to low; when the voltage of the DC bus capacitor meets the grid-connected voltage, obtaining the voltage information of the grid, generating a corresponding three-phase modulation wave, and performing open-loop control on the DC / AC inverter circuit according to the three-phase modulation wave; when the voltage information of the filter capacitor meets the set first grid-connected requirement, closing the grid-connected switch and performing current single closed-loop control on the DC / AC inverter circuit; adjusting the current command, detecting the grid current, when the grid-connected current meets the set second grid-connected requirement, the DC / AC inverter circuit performs double-loop control, and according to the N open-circuit voltages sorted from high to low, starting the corresponding DC / DC boost circuits one by one to perform maximum power tracking control, so that the impact of the grid-connected current is smaller and the soft start effect is better.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic inverters, and particularly relates to a soft-start method, device, and storage medium for a string-type photovoltaic grid-connected inverter. Background Art

[0002] The system structure of a string-type photovoltaic grid-connected inverter adopts a basic structure of pre-stage boost plus post-stage inversion and grid connection. Among them, a DC / DC boost conversion circuit is configured for each photovoltaic string in the pre-stage, and power coupling is performed through a common DC bus capacitor; in the post-stage, a common DC / AC circuit is used to convert direct current into alternating current consistent with the grid voltage. During the startup process of the system, since the grid voltage and the output voltage of the DC / AC inverter circuit may not be exactly the same, if the control is improper, a huge inrush current will occur at the moment when the grid connection switch is closed, which will have an adverse impact on the safe and reliable operation of the system and the power grid. In the prior art, a starting resistor is connected in series on the grid connection side to reduce the inrush current, but this method not only increases losses but also increases the system cost. Summary of the Invention

[0003] The object of the present invention is to provide a soft-start method, device, and storage medium for a string-type photovoltaic grid-connected inverter to solve one or more technical problems existing in the prior art, and at least provide a beneficial choice or create conditions.

[0004] The solution of the present invention to solve its technical problems is: providing a soft-start method, device, and storage medium for a string-type photovoltaic grid-connected inverter.

[0005] According to an embodiment of the first aspect of the present invention, a soft-start method for a string-type photovoltaic grid-connected inverter is provided, including the following steps:

[0006] Connect N photovoltaic strings to the corresponding DC / DC boost circuits and disconnect the grid connection switch;

[0007] Obtain the open-circuit voltage of each photovoltaic string to obtain N open-circuit voltages, and sort the N open-circuit voltages from high to low;

[0008] Obtain the voltage of the DC bus capacitor and determine whether the voltage of the DC bus capacitor meets the grid connection voltage;

[0009] If so, obtain the voltage information of the power grid, generate a corresponding three-phase modulation wave using the voltage information of the power grid, and perform open-loop control on the DC / AC inverter circuit according to the three-phase modulation wave, wherein a filter capacitor is provided at the output end of the DC / AC inverter circuit;

[0010] Obtain the voltage information of the filtering capacitor, and determine whether the voltage information of the filtering capacitor meets the set first grid connection requirement;

[0011] If so, close the grid connection switch and perform current single closed-loop control on the DC / AC inverter circuit;

[0012] Adjust the current command, obtain the grid-connected current according to the adjusted current command, and determine whether the grid-connected current meets the set second grid connection requirement;

[0013] If so, perform double-loop control on the DC / AC inverter circuit, and start the corresponding DC / DC boost circuit one by one according to the N open-circuit voltages sorted from high to low, so that it performs maximum power tracking control.

[0014] Further, the determination of whether the voltage of the DC bus capacitor meets the grid connection voltage specifically includes:

[0015] Determine whether the voltage of the DC bus capacitor is higher than the minimum DC voltage required for grid connection.

[0016] Further, when the voltage of the DC bus capacitor is lower than the minimum DC voltage required for grid connection, it further includes:

[0017] Select the PV string with the highest open-circuit voltage as the starting source according to the N open-circuit voltages sorted from high to low;

[0018] Perform voltage closed-loop control on the DC / DC boost circuit corresponding to the PV string with the highest open-circuit voltage, and input the minimum DC voltage required for grid connection as the voltage command.

[0019] Further, the obtaining of the voltage information of the power grid, using the voltage information of the power grid to generate a corresponding three-phase modulation wave, and performing open-loop control on the DC / AC inverter circuit according to the three-phase modulation wave specifically includes:

[0020] Obtain the voltage amplitude, voltage phase and voltage frequency of the power grid, and calculate and generate a three-phase modulation wave with the same voltage amplitude, voltage phase and voltage frequency as the power grid;

[0021] According to the three-phase modulation wave, the DC / AC inverter circuit performs voltage open-loop control to track the voltage information of the power grid.

[0022] Further, the obtaining of the voltage information of the filtering capacitor, and the determination of whether the voltage information of the filtering capacitor meets the set first grid connection requirement specifically includes:

[0023] Obtain the voltage amplitude, voltage phase and voltage frequency of the filtering capacitor;

[0024] When the voltage amplitude, voltage phase, and voltage frequency of the filter capacitor are equal to or infinitely close to those of the power grid, it is considered that the voltage information of the filter capacitor meets the set first grid connection requirement.

[0025] Further, for the adjusted current command, based on the adjusted current command, obtaining the grid-connected current and determining whether the grid-connected current meets the set second grid connection requirement specifically includes:

[0026] According to the set step size, the current command gradually increases from zero. Based on the increasing current command, the grid-connected current is obtained until the grid-connected current is equal to the set current.

[0027] When the grid-connected current remains equal to the set current within three to five power frequency cycles, it is considered that the grid-connected current meets the set second grid connection requirement.

[0028] Further, the DC / AC inverter circuit performs double-loop control. According to the N open-circuit voltages sorted from high to low, the corresponding DC / DC boost circuits are started one by one to perform maximum power tracking control, which specifically includes:

[0029] The DC / AC inverter circuit performs voltage outer-loop control and current inner-loop control.

[0030] According to the order of the N open-circuit voltages from high to low, the open-circuit voltages are input into the corresponding DC / DC boost circuits one by one.

[0031] The corresponding DC / DC boost circuits are started one by one and perform maximum power tracking control one by one.

[0032] Further, the set current is 1 / N of the minimum current for grid-connected operation.

[0033] According to an embodiment of the second aspect of the present invention, an electronic device is provided, including:

[0034] A memory for storing programs; a processor for executing the programs stored in the memory. When the processor executes the programs stored in the memory, the processor is used to execute a soft-start method of a string-type photovoltaic grid-connected inverter as described in any one of the first aspect.

[0035] According to an embodiment of the third aspect of the embodiments of the present invention, a storage medium is provided, including: computer-executable instructions stored, and the computer-executable instructions are used to execute a soft-start method of a string-type photovoltaic grid-connected inverter as described in any one of the first aspect.

[0036] The beneficial effects of the present invention are as follows: The present invention first adjusts the voltage output of the DC / AC inverter circuit, then adjusts the current output of the DC / AC inverter circuit, and finally determines the control mode of the DC / AC inverter circuit and determines the DC / DC boost circuits for gradually starting N photovoltaic strings to perform maximum power tracking control one by one. Through the above steps, the impact of the grid-connected current is smaller and the soft-start effect is better. Moreover, compared with the present invention, by starting the DC / DC boost circuit targeted according to the voltage of the DC bus capacitor, the input voltage range is wider and the practicability is stronger. It effectively realizes the effective suppression of the starting inrush current of the string-type photovoltaic grid-connected inverter and avoids the adverse effects of the inrush current on the photovoltaic power generation equipment and the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 FIG. is a schematic flowchart of a soft-start method for a string-type photovoltaic grid-connected inverter provided by an embodiment of the present invention;

[0038] Figure 2 FIG. is a schematic diagram of the system framework of a string-type photovoltaic inverter provided by another embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be construed as a limitation of the present invention.

[0040] It should be noted that although the functional modules are divided in the system schematic diagram, in some cases, the steps shown or described may be executed differently from the module division in the system or the sequence in the flowchart. Terms such as "first" and "second" in the specification, claims and the above drawings are used to distinguish similar objects and do not necessarily have to be used to describe a specific order or sequence.

[0041] In the description of the present invention, it should be noted that unless otherwise clearly defined, words such as "set", "installed", and "connected" should be understood in a broad sense. Those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0042] The system structure of the string-type photovoltaic grid-connected inverter is as Figure 2As shown, the basic structure of pre-boosting and post-inverting grid connection is adopted. There are N photovoltaic strings in the string-type photovoltaic grid-connected inverter. A DC / DC boost conversion circuit is configured for each photovoltaic string and coupled through a common DC bus capacitor C1. The post-stage uses a common DC / AC inverter circuit to convert the direct current at the DC bus into alternating current consistent with the grid voltage. The output ends of the common DC / AC inverter circuit are respectively connected to a filter capacitor C2 and a grid connection switch K. Among them, the string-type photovoltaic grid-connected inverter in the present invention is a two-stage string-type three-phase photovoltaic grid-connected inverter.

[0043] According to an embodiment of the first aspect of the present invention, with reference to Figure 1 and Figure 2 , in some embodiments of the present invention, a soft-start method for a string-type photovoltaic grid-connected inverter includes the following steps:

[0044] S100, Connect the N photovoltaic strings to the corresponding DC / DC boost circuits and disconnect the grid connection switch;

[0045] In this embodiment, it is necessary to ensure that the N photovoltaic strings have been connected to the corresponding DC / DC boost conversion circuits and the grid connection switch K is in the off state before starting the three-phase photovoltaic grid-connected inverter.

[0046] S200, Obtain the open-circuit voltage of each photovoltaic string, obtain N open-circuit voltages, and sort the N open-circuit voltages from high to low;

[0047] In this embodiment, detect the open-circuit voltage of each photovoltaic string, obtain N open-circuit voltages, and sort the obtained N open-circuit voltages in descending order.

[0048] S300, Obtain the voltage of the DC bus capacitor and determine whether the voltage of the DC bus capacitor meets the grid connection voltage;

[0049] In this embodiment, detect the voltage of the DC bus capacitor C1, compare the obtained voltage of the DC bus capacitor C1 with the minimum DC voltage required for grid connection, and start the DC / DC boost conversion circuit accordingly based on the comparison result.

[0050] It should be noted that this step can also be achieved by comparing the N open-circuit voltages obtained in S100 with the minimum start-up voltage required for the DC bus. When all N open-circuit voltages have exceeded the minimum start-up voltage required for the DC bus C1, there is no need to start the DC / DC boost conversion circuit and the next step can be directly carried out. Therefore, the present invention can start the DC / DC boost conversion circuit in a targeted manner, with a wider voltage range input to the string-type photovoltaic grid-connected inverter and stronger practicability.

[0051] S310. If so, obtain the voltage information of the power grid, generate corresponding three-phase modulation waves using the voltage information of the power grid, and perform open-loop control on the DC / AC inverter circuit according to the three-phase modulation waves.

[0052] In this embodiment, when the voltage of the DC bus capacitor obtained in S300 already meets the grid connection voltage, the voltage of the power grid is detected to obtain the corresponding voltage information. The controller calculates and generates corresponding three-phase modulation waves according to the obtained voltage information. Through the calculated three-phase modulation waves, the controller generates switching signals to perform open-loop control on the subsequent DC / AC inverter circuit, so as to be able to track the voltage of the power grid. That is to say, the same three-phase modulation waves are obtained through processing based on the voltage information of the power grid, and the output voltage of the DC / AC inverter circuit is adjusted by closed-loop control through the three-phase modulation waves to realize the offset of the output voltage towards the voltage of the power grid.

[0053] S400. Obtain the voltage information of the filter capacitor, and determine whether the voltage information of the filter capacitor meets the set first grid connection requirement.

[0054] In this embodiment, open-loop control of the DC / AC inverter circuit is used to track the voltage of the power grid. The voltage information of the filter capacitor C2 at the output end of the DC / AC inverter circuit is detected, that is, the output voltage of the DC / AC inverter circuit after open-loop control is detected. Judgment is made according to the obtained voltage information whether it meets the set first grid connection requirement. That is, judgment is made according to the output voltage of the DC / AC inverter circuit after open-loop control obtained whether it is consistent with the voltage information output by the power grid.

[0055] S410. If so, close the grid connection switch and perform current single closed-loop control on the DC / AC inverter circuit.

[0056] In this embodiment, it is determined that the voltage information of the filter capacitor meets the set first grid connection requirement. That is, when the output voltage of the DC / AC inverter circuit meets the voltage to be output by the power grid, the grid connection switch K is closed. The controller converts the DC / AC inverter circuit to current single closed-loop control, so as to adjust the output current.

[0057] S500. Adjust the current command, obtain the grid connection current according to the adjusted current command, and determine whether the grid connection current meets the set second grid connection requirement.

[0058] In this embodiment, the current command input by the controller to the DC / AC inverter circuit is adjusted. Through the adjusted current command, the current output by the DC / AC inverter circuit changes. At this time, the grid connection switch has been closed, and the current after grid connection is detected to confirm whether the current after grid connection meets the second grid connection requirement, that is, to confirm whether the current after grid connection conforms to the grid current to be output.

[0059] S510. If so, the DC / AC inverter circuit performs dual-loop control. According to the N open-circuit voltages sorted from high to low, the corresponding DC / DC boost circuits are started one by one to perform maximum power tracking control.

[0060] In this embodiment, it is determined through S500 that when the grid-connected switch K is closed and the output grid-connected current meets the requirements of the second grid connection, the DC / AC inverter circuit is switched to the dual-loop control mode. According to the N open-circuit voltages sorted in S100, the DC / DC boost conversion circuits are started one by one from high to low. The N started DC / DC boost conversion circuits enable all N DC / DC boost conversion circuits to operate in the maximum power tracking control mode. Thus, the soft start of the two-stage string-type three-phase photovoltaic grid-connected inverter is achieved.

[0061] For example: there are 10 photovoltaic strings. The open-circuit voltage with the maximum value is the first photovoltaic string, and the open-circuit voltage with the minimum value is the tenth photovoltaic string. The highest open-circuit voltage is input to the first photovoltaic string, and the first photovoltaic string is made to operate in the maximum power tracking control mode. Then, the second-highest open-circuit voltage is input to the corresponding photovoltaic string, and the corresponding photovoltaic string is made to operate in the maximum power tracking control mode, and so on, until the open-circuit voltage with the minimum value is input to the tenth photovoltaic string, and the tenth photovoltaic string is made to operate in the maximum power tracking control mode. Thus, the N DC / DC boost conversion circuits are started step by step, resulting in a smaller impact on the grid-connected current and a better soft start effect.

[0062] Compared with the prior art of directly starting the outputs of all photovoltaic strings, the present invention first adjusts the voltage output of the DC / AC inverter circuit through S300 and S310, then adjusts the current output of the DC / AC inverter circuit through S400 and S410, and finally adjusts the control mode of the DC / AC inverter circuit through S500 and S510, and determines to gradually start the DC / DC boost conversion circuits of the N photovoltaic strings to perform maximum power tracking control one by one. Through the above steps, the impact on the grid-connected current is smaller and the soft start effect is better. And compared with the prior art of directly using the open-circuit voltage as the starting source, the present invention takes into account the relationship between the minimum starting voltage of the DC bus capacitor and the N open-circuit voltages, and starts the DC / DC boost conversion circuits in a targeted manner, resulting in a wider input voltage range and stronger practicability. The effective suppression of the starting inrush current of the string-type photovoltaic grid-connected inverter is effectively achieved, avoiding the adverse effects of the inrush current on the photovoltaic power generation equipment and the power grid.

[0063] Refer to Figure 2 , in some embodiments of the present invention, the judgment process of S300 specifically includes:

[0064] S301, determine whether the voltage of the detected DC bus capacitor C1 is higher than the minimum DC voltage required for grid connection.

[0065] In this embodiment, the voltage of the detected DC bus capacitor C1 is compared with the minimum DC voltage required for grid connection to confirm whether the voltage of the DC bus capacitor C1 is higher than the required voltage for grid connection.

[0066] It should be noted that in this embodiment, the determination process can also be carried out by comparing the N open-circuit voltages obtained in S100 with the minimum starting voltage required for the DC bus. If all of the N open-circuit voltages have exceeded the minimum starting voltage required for the DC bus C1, then there is no need to start the DC / DC boost conversion circuit and the next step can be directly carried out. Compared with the prior art that directly uses the open-circuit voltage as the starting source, the present invention takes into account the relationship between the minimum starting voltage of the DC bus capacitor and the N open-circuit voltages, and starts the DC / DC boost conversion circuit in a targeted manner, so that the input voltage range is wider and the practicability is stronger.

[0067] Refer to Figure 2 , in some embodiments of the present invention, the determination result of S300 further includes:

[0068] S320, select the PV string corresponding to the maximum open-circuit voltage as the starting source through the N open-circuit voltages sorted from high to low obtained in S200.

[0069] S321, perform voltage closed-loop control on the DC / DC boost conversion circuit corresponding to the PV string in S320, and the controller voltage input command is the minimum DC voltage required for grid connection.

[0070] In this embodiment, if the voltage of the DC bus capacitor C1 is lower than the minimum DC voltage required for grid connection, then the PV string with the highest open-circuit voltage is obtained through the open-circuit voltages sorted from high to low in S200. According to S200, one open-circuit voltage corresponds to one PV string and one DC / DC boost conversion circuit. According to the maximum value of the open-circuit voltage, the corresponding DC / DC boost conversion circuit is started to operate in the voltage closed-loop mode, and the voltage input command of the controller is the minimum DC voltage required for grid connection. Thereby, the voltage of the DC bus capacitor C1 is raised.

[0071] For example: when the open-circuit voltage of the maximum value is the first PV string, the first PV string is used as the starting source to start the DC / DC boost conversion circuit corresponding to the first PV string to operate in the voltage closed-loop mode, and the controller voltage input command is the minimum DC voltage required for grid connection.

[0072] Compared with directly starting all photovoltaic outputs in the prior art, the present invention compares the voltage of the DC bus capacitor C1 with the minimum DC voltage required for grid connection, and sets two starting modes according to the comparison result. When the voltage of the DC bus capacitor C1 is lower than the minimum DC voltage required for grid connection, a photovoltaic string corresponding to the open-circuit voltage of the maximum value is used as the starting source, and the corresponding DC / DC boost conversion circuit is started. Then, a voltage command is input by the controller to start the remaining DC / DC boost conversion circuits. When the voltage of the DC bus capacitor C1 is higher than the minimum DC voltage required for grid connection, at this time, there is no need to start the DC / DC boost conversion circuit, and the DC / AC inverter circuit is regulated according to the detected grid voltage information. The present invention selectively starts the DC / DC boost conversion circuit, making the voltage range input to the inverter wider and the practicability stronger.

[0073] Referring to Figure 2 , in some embodiments of the present invention, the specific implementation process of S310 includes:

[0074] S311, collect the voltage information of the grid. Among them, the voltage information of the grid includes: voltage phase, voltage amplitude, and voltage frequency, and calculate and generate a three-phase modulation wave identical to the voltage information of the grid.

[0075] S312, using the three-phase modulation wave obtained in S311, the DC / AC inverter circuit performs voltage open-loop control to track the voltage information of the grid.

[0076] In this embodiment, the voltage of the grid is sampled to obtain the voltage information of the grid, that is, the phase, amplitude, and frequency of the grid voltage are obtained. According to the obtained voltage phase, amplitude, and frequency, a three-phase modulation wave is calculated and generated. A switching signal is generated through the three-phase modulation wave, and the controller controls the DC / AC inverter circuit to perform voltage open-loop control, thereby tracking the voltage information of the grid. That is to say, in this embodiment, when the voltage of the DC bus capacitor obtained in S300 already meets the grid connection voltage, the voltage of the grid is detected to obtain the phase, amplitude, and frequency of the grid voltage. According to the phase, amplitude, and frequency of the grid voltage, the same three-phase modulation wave is obtained through processing. Through the three-phase modulation wave, the output voltage of the DC / AC inverter circuit is closed-loop controlled to achieve tracking of the voltage information of the grid, and the output voltage of the DC / AC inverter circuit approaches the voltage of the grid.

[0077] Referring to Figure 2 , in some embodiments of the present invention, the judgment process of S400 specifically includes:

[0078] S401, detect the voltage information of the filter capacitor C2. Among them, the voltage information of the filter capacitor C2 includes: voltage phase, voltage amplitude, and voltage frequency;

[0079] S402. When the voltage information of the filter capacitor C2 obtained in S401 is close to the voltage information of the power grid, it is considered that the voltage information of the filter capacitor C2 meets the set first grid connection requirement.

[0080] In this embodiment, it can be seen from S310 that the DC / AC inverter circuit realizes the tracking of the voltage of the power grid through open-loop control, and the output voltage of the DC / AC inverter circuit changes. Collecting the filtered voltage information can reduce noise interference and improve the comparison accuracy in S420. The voltage information of the filter capacitor C2 includes: voltage phase, voltage amplitude, and voltage frequency. When the phase, amplitude, and frequency of the voltage of the filter capacitor C2 are equal to or infinitely close to the phase, amplitude, and frequency of the power grid voltage, it is considered that the phase, amplitude, and frequency of the voltage of the filter capacitor C2 meet the set first grid connection requirement.

[0081] It should be noted that when the difference between the voltage information of the filter capacitor C2 and the voltage information of the power grid is too large, and the difference between the two is greater than the set difference threshold, it is considered that the voltage information of the filter capacitor C2 does not meet the set first grid connection requirement. At this time, return to S310 to track the voltage information of the power grid.

[0082] Refer to Figure 2 , in some embodiments of the present invention, the judgment process of S500 specifically includes:

[0083] S501. According to the set step size, the current command gradually increases from zero. Through the increased current command, collect the current after grid connection until the grid-connected current is equal to the set current.

[0084] S502. When the grid-connected current continuously equals the set current within three to five power frequency cycles, it is considered that the grid-connected current meets the second grid connection requirement.

[0085] In this embodiment, the grid connection switch K is already closed, and the voltage output by the DC / AC inverter circuit is approximately equal to the voltage of the power grid. Adjust the current command input to the DC / AC inverter circuit. The current command gradually increases from zero according to the set step size, and the grid-connected current also increases as the current command increases. When the grid-connected current increases to the set current, the current command stops increasing. Confirm whether the grid-connected current continuously equals the set current within 3 to 5 power grid power frequency cycles. When the grid-connected current is stable at the set current and maintained for 3 to 5 power grid power frequency cycles, it is considered that the grid-connected current meets the second grid connection requirement.

[0086] It should be noted that the set current is 1 / N of the minimum current during grid-connected operation. That is to say, the current command input to the DC / AC inverter circuit is adjusted, and the current command increases from zero until the grid-connected current is equal to 1 / N of the minimum current during grid-connected operation. When the grid-connected current stabilizes at 1 / N of the minimum current during grid-connected operation and maintains for 3 to 5 power grid power frequency cycles, it is considered that the grid-connected current meets the second grid-connection requirement.

[0087] Among them, when the second grid-connection requirement in S502 is not met, it returns to S501 to adjust the input current command again.

[0088] Refer to Figure 2 , in some embodiments of the present invention, the specific implementation process of S510 includes:

[0089] S511, the DC / AC inverter circuit is switched to voltage outer closed-loop control and current inner-loop control.

[0090] S512, according to the order of the N open-circuit voltages from high to low in S200, each open-circuit voltage is input to the corresponding DC / DC boost conversion circuit one by one.

[0091] S513, the corresponding DC / DC boost conversion circuit is started one by one and operates in maximum power point tracking control one by one.

[0092] In this embodiment, it is judged through S500 that when the grid-connected switch K is closed and the output grid-connected current meets the second grid-connection requirement, the DC / AC inverter circuit is switched to voltage outer closed-loop control and current inner-loop control mode. According to the N open-circuit voltages sorted in S200, the controller inputs each sorted open-circuit voltage to the corresponding DC / DC boost conversion circuit one by one, and starts the DC / DC boost conversion circuits one by one from high to low, making them work in maximum power point tracking control mode. Thus, the soft start of the two-stage string-type three-phase photovoltaic grid-connected inverter is realized.

[0093] For example: there are 10 photovoltaic strings, the open-circuit voltage of the maximum value is the first photovoltaic string, and the open-circuit voltage of the minimum value is the tenth photovoltaic string. The highest open-circuit voltage is input to the first photovoltaic string, and the first photovoltaic string operates in maximum power point tracking control mode. Then the second highest open-circuit voltage is input to its corresponding photovoltaic string, and the corresponding photovoltaic string operates in maximum power point tracking control mode, and so on, until the minimum open-circuit voltage is input to the tenth photovoltaic string, and the tenth photovoltaic string operates in maximum power point tracking control mode. Thus, after the grid-connected switch is closed, the N DC / DC boost conversion circuits are gradually started, making the impact of the grid-connected current smaller and the soft start effect better.

[0094] According to an embodiment of the second aspect of the present invention, an electronic device includes: a memory for storing programs. A processor is configured to execute the programs stored in the memory. When the processor executes the programs stored in the memory, the processor is configured to execute the soft start method of a string-type photovoltaic grid-connected inverter according to the first aspect.

[0095] The processor and the memory may be connected through a bus or other means.

[0096] The memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs, such as the soft start method for a string-type photovoltaic grid-connected inverter described in the embodiments of the present invention. By running the non-transitory software programs and instructions stored in the memory, the processor realizes the soft start method of a string-type photovoltaic grid-connected inverter according to the embodiments of the first aspect of the present invention.

[0097] The memory may include a program storage area and a parameter storage area. Among them, the program storage area can store an operating system and application programs required for at least one function; the parameter storage area can store the soft start method for the above-mentioned string-type photovoltaic grid-connected inverter. In addition, the memory may include a high-speed random access memory and may also include a non-transitory memory, such as at least one magnetic disk storage device, a flash memory device, or other non-transitory solid-state storage devices. In some embodiments, the memory may optionally include a memory remotely provided with respect to the processor, and these remote memories can be connected to the processor through a network. Examples of the above-mentioned network include but are not limited to the Internet, an enterprise intranet, a local area network, a mobile communication network, and combinations thereof.

[0098] The non-transitory software programs and instructions required to implement the above-mentioned terminal selection method are stored in the memory and, when executed by one or more processors, execute the soft start method of a string-type photovoltaic grid-connected inverter according to the first aspect of the present invention.

[0099] According to an embodiment of the third aspect of the present invention, the present invention further provides a storage medium storing computer-executable instructions for executing the soft start method of a string-type photovoltaic grid-connected inverter according to the first aspect.

[0100] Those of ordinary skill in the art will appreciate that all or some of the steps and systems disclosed above can be implemented as software, firmware, hardware, and appropriate combinations thereof. Some or all of the physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or as hardware, or as an integrated circuit, such as an application specific integrated circuit. Such software can be distributed on a computer-readable medium, which can include a computer storage medium (or non-transitory medium) and a communication medium (or transitory medium). As is well known to those of ordinary skill in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVDs) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by a computer. In addition, it is well known to those of ordinary skill in the art that communication media typically includes computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and can include any information delivery media.

[0101] The above has specifically described the preferred embodiments of the present invention. However, the present invention is not limited to the described embodiments. Those skilled in the art can also make various equivalent variations or substitutions without departing from the spirit of the present invention. These equivalent variations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A soft start method for a string-type photovoltaic grid-connected inverter, characterized in that, Including: Connect N photovoltaic strings to the corresponding DC / DC boost circuits and disconnect the grid-connected switch; Obtain the open-circuit voltage of each photovoltaic string to get N open-circuit voltages, and sort the N open-circuit voltages from high to low; Obtain the voltage of the DC bus capacitor and determine whether the voltage of the DC bus capacitor meets the grid-connected voltage; If so, obtain the voltage information of the grid, generate corresponding three-phase modulation waves using the voltage information of the grid, and perform open-loop control on the DC / AC inverter circuit according to the three-phase modulation waves, where a filter capacitor is provided at the output end of the DC / AC inverter circuit; Obtain the voltage information of the filter capacitor and determine whether the voltage information of the filter capacitor meets the set first grid-connection requirement; If so, close the grid-connected switch and perform current single closed-loop control on the DC / AC inverter circuit; Adjust the current command, obtain the grid-connected current according to the adjusted current command, and determine whether the grid-connected current meets the set second grid-connection requirement; If so, perform double-loop control on the DC / AC inverter circuit, and start the corresponding DC / DC boost circuits one by one according to the N open-circuit voltages sorted from high to low to perform maximum power tracking control.

2. The soft start method of a string-type photovoltaic grid-connected inverter according to claim 1, characterized in that The determination of whether the voltage of the DC bus capacitor meets the grid-connected voltage specifically includes: Determine whether the voltage of the DC bus capacitor is higher than the minimum DC voltage required for grid connection.

3. The soft start method of a string type photovoltaic grid-connected inverter according to claim 2, characterized in that, When the voltage of the DC bus capacitor is lower than the minimum DC voltage required for grid connection, it further includes: Select the photovoltaic string with the highest open-circuit voltage as the starting source according to the N open-circuit voltages sorted from high to low; Perform voltage closed-loop control on the DC / DC boost circuit corresponding to the photovoltaic string with the highest open-circuit voltage, and input the minimum DC voltage required for grid connection as the voltage command.

4. The soft start method of a string-type photovoltaic grid-connected inverter according to claim 1, characterized in that, The obtaining of the voltage information of the grid, generating corresponding three-phase modulation waves using the voltage information of the grid, and performing open-loop control on the DC / AC inverter circuit according to the three-phase modulation waves specifically includes: Obtain the voltage amplitude, voltage phase and voltage frequency of the grid, and calculate and generate three-phase modulation waves with the same voltage amplitude, voltage phase and voltage frequency as those of the grid; According to the three-phase modulation waves, the DC / AC inverter circuit performs voltage open-loop control to track the voltage information of the grid.

5. The soft start method of a string type photovoltaic grid-connected inverter according to claim 4, characterized in that, The obtaining of the voltage information of the filter capacitor and determining whether the voltage information of the filter capacitor meets the set first grid-connection requirement specifically includes: Obtain the voltage amplitude, voltage phase and voltage frequency of the filter capacitor; When the voltage amplitude, voltage phase and voltage frequency of the filter capacitor are equal to or infinitely close to the voltage amplitude, voltage phase and voltage frequency of the grid, it is considered that the voltage information of the filter capacitor meets the set first grid-connection requirement.

6. The soft start method of a string-type photovoltaic grid-connected inverter according to claim 1, characterized in that The adjustment of the current command, obtaining the grid-connected current according to the adjusted current command, and determining whether the grid-connected current meets the set second grid-connection requirement specifically includes: The current command gradually increases from zero according to the set step size, and the grid-connected current is obtained according to the increased current command until the grid-connected current is equal to the set current; When the grid-connected current remains equal to the set current within three to five power frequency cycles, it is considered that the grid-connected current meets the set second grid-connection requirement.

7. The soft start method of a string-type photovoltaic grid-connected inverter according to claim 1, characterized in that, The DC / AC inverter circuit performs double-loop control. According to the N open-circuit voltages sorted from high to low, the corresponding DC / DC boost circuits are started one by one to perform maximum power tracking control, which specifically includes: The DC / AC inverter circuit performs voltage outer closed-loop control and current inner closed-loop control; In the order of the N open-circuit voltages from high to low, the open-circuit voltages are input to the corresponding DC / DC boost circuits one by one; The corresponding DC / DC boost circuits are started one by one and perform maximum power tracking control one by one.

8. The soft start method of a string-type photovoltaic grid-connected inverter according to claim 6, characterized in that, The set current is 1 / N of the minimum current for grid-connected operation.

9. An electronic device, characterized in that, Including: A memory for storing programs; A processor for executing the programs stored in the memory. When the processor executes the programs stored in the memory, the processor is used to execute a soft-start method for a string-type photovoltaic grid-connected inverter as described in any one of claims 1 to 8.

10. A storage medium, characterized in that, Including: Stored with computer-executable instructions for executing a soft-start method for a string-type photovoltaic grid-connected inverter as described in any one of claims 1 to 8.

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